Add BundleClient API for basic commands

Haven't written out the API for the permissions commands, which are roughly:
  add-group, rm-group, add-user, rm-user, chmod, chgrp
or the remote / local sync commands, which are roughly:
  add-remote, add-group, import, sync

My next step is writing the LocalBundleClient, which will implement all of the basic commands. When that's done, it'll basically provide the same functionality as Percy's prototype, but with a cleaner architecture and support for a few more features (better command parsing, metadata, search, etc).