0.5 release notes draft

## Major Themes

Rook v0.5 is a milestone release that improves reliability, adds support for newer versions of Kubernetes, picks up the latest stable release of Ceph (luminous), and makes a number architectural changes that pave the way to getting to Beta and adding support for other storage back-ends beyond Ceph.

## Attention needed

Rook does not yet support upgrading a cluster in place. To upgrade from 0.4 to 0.5 we recommend you tear down your cluster and install Rook 0.5 fresh.

We now publish the rook containers to quay.io and docker hub. Docker hub support multi-arch containers so a simple `docker pull rook/rook` will bring the right images for any of the supported architectures. We will continue to publish quay.io for continuity.

Rook no longer runs as a single binary. For standalone mode we now require a container runtime. We now only publish containers for Rook daemons. Client tools are still release in binary form.

There is a new release site for Rook that https://release.rook.io that contains all binaries, images, yaml files, test results etc.

## Known Issues

If you shutdown a Rook cluster without first unbinding persistent volumes, the volumes might be stuck indefinitely and require a host reboot to get cleared. See #376.

## Notable Features

### Kubernetes
- Support for Kubernetes 1.7 and switched to CRDs from TPRs
- Names of the deployments, services, daemonsets, pods, etc are named more consistently, for example, rook-ceph-mon, rook-ceph-osd, rook-ceph-mgr, rook-ceph-rgw, rook-ceph-mds
- [Node affinity and Tolerations](https://github.com/rook/rook/blob/master/Documentation/cluster-tpr.md#placement-configuration-settings) added to the Cluster TPR for api, mon, osd, mds, and rgw
- Each mon is managed with a replicaset
- New Rook Operator [Helm chart](https://github.com/rook/rook/blob/master/demo/helm/rook-operator/README.md)
- A ConfigMap can be used to [override Ceph settings](https://github.com/rook/rook/blob/master/Documentation/advanced-configuration.md#custom-cephconf-settings) in the daemons

### Ceph
- Ceph Luminous is now the default version used by Rook. Luminous is the basis of a LTS release of Ceph and introduces bluestore which improves performance.
- Ceph is no longer compiled into Rook as a static library, instead we package a streamlined version of Ceph into our containers and call the ceph daemons and tools directly.
- Ceph Kraken is no longer supported.

### Tools
- The client binary `rook` was renamed to `rookctl`
- The damemon binary was renamed from `rookd` to `rook`
- The `rook-client` container is no longer built. Run the [toolbox container](https://github.com/rook/rook/blob/master/Documentation/toolbox.md) for access to the `rookctl` tool.
- `amd64`, `arm`, and `arm64` supported by the toolbox in addition to the daemons

### Build and Test
- No more git submodules
- Added support for armhf (experimental)
- Faster incremental image builds based on caching
- E2E Integration tests for Block, File, and Object
- Functional Tests for Block store
- Block store long haul testing