EventDispatcher ISIN filter now works
EntityGroup changes

Setting dropper type now works and the entity display thing tells
you all the dropper types.
You can now touch entities that aren't solid
dusk.behave.Pickup is now savable.
Started work on checkpoints

They work at a basic level, but I want entity behaviours with
checkpoints to know if they are active or not. Also, checkpoints
should be savable.