feat(controller): check client against API version

Before locking the API version, we needed some way to ensure that
we did not break the client. This was done by comparing the client's
version against the server. If there was a mismatch on the minor or
major release versions (as noted in Semver 2.0.0[1]), the server
would refuse the request. Because we have locked the API version,
it would make sense to test against that to see if the client is
compatible with the API. If not, then the client should upgrade.

This also modifies the current behaviour to warn the user on a minor
version mismatch. If there is a minor version mismatch between the
client and the server, it will press onwards and display a warning,
advising the user to upgrade. If there is a major version mismatch,
then the API server will refuse the request as before.

[1]: http://semver.org/
feat(controller): add X_DEIS_PLATFORM_VERSION header in response
chore(release): bump controller API to v1.1
feat(CONTRIBUTING): add design proposal guidelines

ripped straight from https://github.com/docker/docker/blob/master/CONTRIBUTING.md#design-and-cleanup-proposals
chore(Makefile): update development registry image to v0.9.0 tag
feat(user-data): enable time synchronization on startup
ref(contrib/coreos): clean up time sync
Merge pull request #2596 from carmstrong/pr-2563

feat(contrib/coreos): enable time synchronization on startup
Merge pull request #2567 from bacongobbler/2548-api-version

feat(controller): check client against API version
Merge pull request #2592 from mboersma/bump-dev-registry-0.9.0

chore(Makefile): update development registry image to v0.9.0 tag
Merge pull request #2576 from bacongobbler/design-proposal

feat(CONTRIBUTING): add design proposal guidelines
ref(Vagrantfile): remove nictype override; virtio is the default