This is the first step preparing for patches and merge requests.
The work-item aspect of MRs will reuse the Ticket related tables, except MRs
will live under repos. So, the context of tickets will no longer be just
projects, but will also be repos.
So, TicketProjectLocal turns into TicketContextLocal, and there are 2 new
tables that refer to it: TicketProjectLocal and TicketRepoLocal. Tickets will
have the former, MRs will have the latter.
