Rename Repository to Registry.
Add the Repository class, have the Registry return these.
Status command: Move functionality to Repository.
Add ffmerge command.

This command automatically merges all remote-tracking branches
in all repositories, but only if the corresponding repository
is clean (i.e., no untracked files, no dirty working directory,
no uncommitted things in the index.)
Merge branch 'feature/ffmerge-command' into develop