Layer visibility changes are now undoable.
Layer name changes are now undoable.
Layers are ordered properly in LayerManagerView (i.e. 0 is now the lowest layer like Tiled).
Layers are ordered properly in MapEditorView (i.e. 0 is now the lowest layer like Tiled).
Raising and lowering layers moved to the MapModel object.
Made undo framework work of aggregator events instead of model events to prevent the undoing from being recorded.