Implement UI for subanalysis mode

Implement UI for subanalysis mode
unfortunately its still only a read-only user interface but
the a user can select a sequence region, add it to our track display
and then either cancel or run the analysis.

It unfortunately blocks the UI while it runs, but there's not a whole lot
I can do about that.

While implementing this I added a number of unittests to make sure
that my sequence selection code workes.