Fixes two bugs:
- When calling the dismiss function it would hang indefinitely if there weren't any tokens on the board to dismiss. This made dismisss-then-summon macros not work the first time.
- Fixes a bug where if you did accidentally summon two things at once then the second one would fail when the first one deleted the highlight layer, leaving around the mouse-move listener spewing errors. Turns out you don't have to destroy the layer at all since adding it will return the existing one if it is there.