REL-1301: QPT now preserves instrument configuration / filtering between...

... refreshes. Also fixed some serious bugs as to how the selection values (selected, unselected, indefinite) in the instrument configuration tree were calculated.
This section is the heart of it, I believe.  From talking to Sebastian I believe it's probably fine to not recreate the model here but thought someone who knows the qpt better than me (that is, anybody else on the team!) should probably confirm.  @fnussber ?