Add properties sendPatchesTo and tracksPatchesFor
These are much like ticketsTrackedBy and tracksTicketsFor, except for
patches and MRs. Allows for similar flexibility pointing to the actor
managing the patch / MR. Typically on web forges a repo actor would
manage its own MRs (and tickets), but the flexibility allows for other,
more loose or varied setups, to be equally able to federate (for example
repos hosted by e.g. gitolite while e.g. Bugzilla handles tickets and
patches).