Rework block matching tuner to be compatible with BlockMatcher classes

The ``StereoBMTuner`` is now a ``BMTuner`` that autodiscovers settable
parameters in the ``BlockMatcher`` that is passed to it.

This makes the code a little shorter and simpler. As long as the
``BlockMatcher`` the ``BMTuner`` receives fulfills the required API
requirements, the ``BMTuner`` can interact with it and creates the
appropriate toolbars needed to tune the ``BlockMatcher``.
Update UI to allow usage of new classes
Bugfix: BlockMatchers now export and import from file correctly
Remove unused function
Allow img_pair_2_ply to use both block matchers