Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.4.24+commit.e67f0147.js&optimize=true&gist=

baseContentManagementContract.sol

pragma solidity ^0.4.24;

import "./sharedTypes.sol";


contract BaseContentManagementContract {
    address internal author;
    SharedTypes.contentType internal typeOfContent;
    uint internal numberOfViews;
    mapping (address => address) viewersList;   // List of user that 
    
    constructor () public {
        author= msg.sender;
        numberOfViews= 0;
    }
}

catalogSmartContract.sol

pragma solidity ^0.4.24;

import "./sharedTypes.sol";
import "./ownable.sol";
import "./contentManagementContracts.sol";


contract CatalogSmartContract is Ownable {
    
    // True if 'selfdestruct' function wasn't called
    bool active= false;
    
    // Users registered to system
    SharedTypes.User [] users;
    // Number of user (also index of next user in the array)
    uint usersCount;
    
    // Contents linked to system
    SharedTypes.ExtendedContent [] contents;
    // Number of contents (also index of next content in the array)
    uint contentsCount;
    
    
    constructor () public {
        active= true;
        usersCount=0;
        contentsCount= 0;
    }
    
    
    
    modifier isActive () {
        require (active == true);
        _;
    }
    
    
    function killMe () public onlyOwner() {
        active= false;
        selfdestruct (owner);
    }
    
    
    
    // Function to register an user to system
    function registerMe () public {
        uint i= usersCount++;
        users[i].addr= msg.sender;
        users[i].accType= SharedTypes.accountType.standard;
    }
    
    
    
    // Function to link a content with the system
    function publishContent (address contentAddr, SharedTypes.contentType t) public {
        uint i= contentsCount++;
        contents[i].content
    }
    
/*    
    // Returns the number of views for each content
    function getStatistics () public view returns (...) {
    }
    
    
    // Returns the list of contents without the number of views
    function getContentList () public view returns (...) {
    }
    
    
    // Returns the list of x newest contents
    function getNewContentList (uint n) public view returns (...) {
    }
    
    
    
    // Returns the most recent content with genre x
    function getLatestByGenre (...) public view returns (...) {
    }
    
    
    
    // Returns the content with genre x, which has received the maximum number of views
    function getMostPopularByGenre (...) public view returns (...) {
    }
    
    
    
    // Returns the most recent content of the author x
    function getLatestByAuthor (...) public view returns (...) {
    }
    
    
    
    // Returns the content with most views of the author x
    function getMostPopularByAuthor (...) public view returns (...) {
    }
    
    
    
    // Returns true if x holds a still valid premium account, false otherwise
    function isPremium (...)  public view returns (...) {
    }
    
    
    /* ********************************************* */
    /* ********************************************* */
    /* ********************************************* */
    
    
    // Pays for access to content x
    /*function getContent (...) public {
    }
    
    
    
    // Requests access to content x without paying, premium accounts only
    function getContentPremium (...) public {
    }
    
    
    
    // Pays for granting access to content x to the user u
    function giftContent (..., ...) public {
    }
    
    
    
    // Pays for granting a Premium Account to the user u
    function giftPremium (...) public {
    }
    
    
    
    // Starts a new premium subscription
    function buyPremium () public {
    }
*/
}

contentManagementContracts.sol

pragma solidity ^0.4.24;

import "./baseContentManagementContract.sol";


contract SongManagementContract is BaseContentManagementContract {
}



/* ********************************************* */
/* ********************************************* */
/* ********************************************* */



contract VideoManagementContract is BaseContentManagementContract {
}



/* ********************************************* */
/* ********************************************* */
/* ********************************************* */



contract PhotoManagementContract is BaseContentManagementContract {
}



/* ********************************************* */
/* ********************************************* */
/* ********************************************* */



contract DocumentManagementContract is BaseContentManagementContract {
}

crowdfund.sol

pragma solidity ^0.4.24;

import "./mortal.sol";


contract Crowdfund {
    struct Funder {
        address addr;
        uint amount;
    }
    
    struct Project {
        bool created;
        bool opened;
        string name;
        address owner;
        mapping (uint => Funder) funders;
        uint fundersSize;
        uint amount;
        uint fundingGoal;
    }
    
    event ProjectCreated (string _name, uint _fundingGoal);
    event FundTransferred (address _backer, string _project, uint _amount, uint _remainingAmount);
    event fundingGoalReached (string project);
    
    
    address private owner;
    mapping (string => Project) private projects;
    
    
    modifier ProjectNotExists (string _name) {
        require (projects[_name].created == false);
        _;
    }
    
    modifier ProjectExists (string _name) {
        require (projects[_name].created == true);
        _;
    }
    
    
    
    constructor () public {
        owner= msg.sender;
    }
    
    
    
    function createProject (string _projectName, uint _amount) public ProjectNotExists (_projectName) {
        projects[_projectName]= Project (true, true, _projectName, msg.sender, 0, 0, _amount);
        emit ProjectCreated (_projectName, _amount);
    }
    
    
    
    function sendMoney (string _projectName, uint _sum) public ProjectExists (_projectName) {
        Project storage p= projects[_projectName];
        p.funders[p.fundersSize]= Funder (msg.sender, _sum);
        p.fundersSize++;
        p.amount += _sum; 
        uint remaining= p.fundingGoal - _sum;
        emit FundTransferred (msg.sender, _projectName, _sum, remaining);
        checkGoalReached (_projectName);
    }
    
    
    
    function checkGoalReached (string _projectName) private returns (bool) {
        Project storage p= projects[_projectName];
        if (p.fundingGoal <= p.amount) {
            emit fundingGoalReached (_projectName);
            p.opened= false;
            return true;
        }
        return false;
    }
    
    
    
    function getProject (string _projectName) public view returns (bool, address, uint, uint, uint, bool) {
        Project storage p= projects[_projectName];
        return (p.opened, p.owner, p.fundersSize, p.amount, p.fundingGoal, p.opened);
    }
}

mortal.sol

pragma solidity ^0.4.24;


contract Mortal {
    address owner;
    
    constructor () public {
        owner= msg.sender;
    }
    
    function kill () public {
        if (msg.sender == owner)
            selfdestruct (owner);
    }
}

ownable.sol

pragma solidity ^0.4.24;


contract Ownable {
    address owner;
    
    constructor () public {
        owner = msg.sender;
    }
    
    modifier onlyOwner () {
        require (msg.sender == owner);
        _;
    }
}

sharedTypes.sol

pragma solidity ^0.4.24;

library SharedTypes {
    
    // Kind of content
    enum contentType {song, video, photo, document}
    
    // Kind of account
    enum accountType {standard, premium}
    
    // Type for registered users, both authors or customers
    struct User {
        address addr;
        accountType accType;
        uint expirationTime;    // Expiration time. Valid only for premium account
    }
    
    // Struct to hold togheter BasContentManagementContracts and list of users which payed to view these contents
    struct ExtendedContent {
        uint totalViews;
        BaseContentManagementContract content;
        mapping (address => bool) viewers;
    }
}