chore(builder): import slug* components

Instead of keeping the projects in their own separate repository,
importing them into deis/builder allows us to version them and keep
them in sync.

Note that we will still need to update our trusted builds for the slug* components on http://registry.hub.docker.com/ to reflect this change. Also note that this is a straight import; we still need to clean out and remove some of the old stuff in there such as the DCOs and the MAINTAINERs files (unless we want to keep them)

refs #1174 (not closing until we update the builds on DockerHub)