Test pickmed branches for conflicts, save results

Create method queued by the pickme servlet that checks that pickme against other
pickmes in the same push. Tag any pickes that fail to merge on top as conflicts
Send email and XMPP notifications on conflict
Display conflict text on website, add tag colours

Encode the 'conflicts' database field into the JSON representation of a request.
Set colours for the conflict-master and conflict-pickme tags
Style the Conflicts section on the request detail div
Switch from Threading to Multiprocess

Avoid global locking if git takes too long
Add pushplan to create Conflicts column in db

Add SQL commands needed to create / rollback the 'Conflicts' column in
the push_requests DB field.
Add thorough submodule conflict detection

Fully flesh out submodule conflict resolution based on the merge-branches push
helper script.
Add no-conflict marker