Fix a bug where the notification could crash the game.

- Remove duplicate button (use DionicSoftware‘s button instead of mine)
- SHIFT+select draws a rectangle on the ground rather than a transparent box (tell me if you like this better or the old one!)
- A number will pop up when you select a new item that tells you its position in the laser‘s queue
- Issue notification when the last target was destroyed
- Minor and mostly invisible bug fixes and improvements