Add some indexes for common cobra/mcs/ag/target joins

One common set of queries is the family of select xxx from cobra_match where mcs_frame_id == yyy . I think we should add an index on mcs_frame_id. FWIW cobra_match has 36M rows and takes 4G of space. Only 2.8s now, but will clearly grow.

And I'll bet that a bit of thought will find a few more of these.