Preliminary implementation of server-side forking (issue 137)

Preliminary implementation of server-side forking (issue 137)

The fork mechanism clones the repository , access restrictions, and
other config options.  The app has been updated throughout to handle
personal repositories and to properly display origin/fork links.

In order to fork a repository the user account must have the #fork role,
the origin repository must permit forking, and the user account must
have standard clone permissions to the repository.

Because forking introduces a new user role no existing user accounts can
automatically begin forking a repository.  This is both a pro and a con.

Since the fork has the same access restrictions as the origin repository,
those who can access the origin may also access the fork.  This is intentional
to facilitate integration-manager workflow.  The fork owner does have the
power to completely change the access restrictions of his/her fork.