Abstracted the input away from hard-coding keys into the game logic. Instead, the game objects just test if an
abstract input event has occured, and the editor defines which keys are actually tested.
Not only does this make the game code cleaner, it makes the user experience better, as it is easy (and therefore likely)
that multiple key combinations can be used.
Rox development, and bug-fixes/improvements to Itchy along the way.
StageConstraint now has the ability to REPLACE actors, and therefore allowing only one actor per grid location.