Make verify realtime

 Run SHA fetching and conflict checking separately
 
SHAs were getting set very slowly since they could be stuck behind conflict
checking jobs in the GitQueue. This caused problems where two verify jobs
could end up both running after an edit, which would raise a GitError, as
well as the issue of external resources reliant on pickme SHA not being usable.
    
This patch breaks the GitQueue into two queues with two workers; one for SHA
fetching, that queries the remote, and one for conflict checking, which uses
the local git repo.