Adding an editor screen. Can't edit levels yet but can load MazeScreen to
test a default stage.
Added serialization and loading of stage and stage objects
Moved stage rendering code to separate class. Made the stage appear on
editor.
Added mouse pointer input, and a cursor to the editor which looks really
bad.
Added code to drag/pan the editor view around
Added code to grab stuff around in the editor
Adding a blueprint-like background to the editor
Added code to add and remove(delete key only) walls, pushers and exits
Added a trash tool
Modified wall tool to create wall "rectangles"
Added code to check whether two objects overlap when dragging them around
Added code to merge walls on editor
Added glue tool
Changed what block is selected when a wall is created
Added ability to save and load stages
Added eraser tool
Added code to change pusher facing towards the direction which its dragged
Added code to enter file names when saving
Fixed mazescreen to not crash when there are no pushers in a stage.
Added a way to keep grabbable properties when creating walls from other
walls