feat(store): add deis-store component

This PR implements the deis-store backing service described in #1384. It is a Dockerified implementation of [Ceph](http://ceph.com).

`deis-store` consists of three components:
**deis-store-monitor**
This container configures and starts a [Ceph monitor](https://ceph.com/docs/v0.85/man/8/ceph-mon/), the bookkeepers of the cluster. We block until there are three monitors running before we proceed with allowing the daemons to come up.

**deis-store-daemon**
This container configures and starts a [Ceph object store daemon](https://ceph.com/docs/v0.85/man/8/ceph-osd/). There are three of these containers at a minimum in a cluster, as data stored in Ceph is configured to be duplicated twice. We allow degraded writes even if just one OSD is up.

**deis-store-gateway**
This container configures and starts [radosgw](https://ceph.com/docs/v0.85/radosgw/), an S3- and Swift-compatible object store. This container is accessible within the cluster via etcd service discovery, as well as externally to the cluster at `http://store.domain.tld`.

This PR also adapts the database and registry (WIP) to use `deis-store` for storing WAL logs/backups and Docker image filesystem layers, respectively.

TESTING:
Testing deis-store will involve a custom-built `deisctl` as implemented in deis/deisctl#96. `deisctl install platform` should then provision and start deis-store.

TODOS:
- [x] `database`: Rewrite logic which checks if the database is already initialized -- we can't test for the existence of /var/lib/postgresql/9.3/main any longer, as we need to run confd before this check happens (mainly so the deis-store-gateway is in /etc/hosts), and confd will template files in this directory. So, we need a better method to determine if the database has already been initialized.
- [x] `database`: configure periodic backups
- [x] `registry`: use the S3 API credentials stored in etcd to store filesystem layers in `deis-store`. We need docker/docker-registry#515.
- [x] No longer install `deis-database-data` or `deis-registry-data` containers
- [x] Test failure and disaster scenarios (stop a container and then start it later, etc.)
- [x] Write integration/component tests
- [x] Update docs anywhere we list the Deis components

closes #1384 
closes #1385 
closes #1906
replaces #1754 
replaces #1803
refs deis/deisctl#96
refs deis/docker-registry#3

[skip ci]
@johanneswuerbach We discussed this and it didn't compile without at least CORS. We're going to leave this in for the PR to land, but if you PR its removal and it works, we'd take the merge.