Some small bug fixes, and also removed the need for casting the 'owner',
by only introducing this field for a subclass of McmcMove, namely
StructAlignMcmcMove.
This branch now running, with results looking reasonable. 

To do:

1) Fix GUI (currently tries to access acceptance rates via a method that
was removed)
2) Test against main structalign branch to make sure everything is
behaving in the same fashion.