Support personal branches

See this comment from another user for details on this feature.

Summary: If a user creates a branch under their username namespace, they automatically get full read/write/delete/rewind privileges to that branch.

For Example:

I make a branches: davidrogers/featureX or p-davidrogers-featureX (different orgs may have different naming conventions)

I can rebase/sync with the master branch, and do a non-fastforward push to davidrogers/featureX. On a long running personal feature branch, it's useful to sync up with master every once in a while.