Restore repository shortcuts, for now

Summary:
These need to die soon since they're not structurally policy-aware, but keep them around for the moment until we can replace them.

There is no UI to create these, and only Facebook has them.

Test Plan: {F57614}

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6920