[swift] Extend NSBundle to get Version and Build info

[swift]NSBundle-version-build.swift

extension NSBundle {
    
    class var versionNumber: String {
        if let version = NSBundle.mainBundle().infoDictionary?["CFBundleShortVersionString"] as? String {
            return version
        }
        return "N.D."
    }
    
    class var buildNumber: String {
        if let build = NSBundle.mainBundle().infoDictionary?["CFBundleVersion"] as? String {
            return build
        }
        return "N.D."
    }
    
    class var versionAndBuild: String{
        return "\(NSBundle.versionNumber)-\(NSBundle.buildNumber)"
    }
}