Implement exclude moves

Implement exclude moves

Dragging a piece by double-clicking it on the from-square in analysis mode
will not perform the entered move, but send an exclude or include command
to the engine for that move (provided the engine enabled this with
feature exclude=1), depending on if the move was already excluded or not.
To this end a map of excluded moves is kept, and cleared when we move to
another position through moving, undo, setboard or new. The user can see
whether he included or excluded the move, as exclude uses premove highlights.
  Commands "exclude|include all" are sent when we throw a double-clicked
piece off board (vertically or horizontally, respectively), but after
exclude all the most recent PV move is included again.
  Remaining problem is that promotions can only be excluded.