added more improvements to the infinite undo and reworked existing undo...

added more improvements to the infinite undo and reworked existing undo actions to conform to the infinite undo model. fixed per-window undo menu updating, finalized undo actions 1,2,3,4,5,9, and 10. Still need 6,7,8 and a new action 11 (namely apply, canvas apply, to front/back, and rename). Also improved paste behavior to make it more user friendly, particularly within the context of infinite undo.