Begun implementation of walls.
Implemented walls. Closes #10
Implemented AP. Closes #9
Implemented AP. Created ActionProvider.
Added visualization of actions.
Fully implemented clicking for actions, displaying actions, action menu, etc. Closes #25
Refactored to improve structure of taking actions. Replaced ActionProvider and SelectSquareListener with ActionPerformer. Added basic behaviour for left-clicking to do a default action.