Allow adding and removing of Level Layers #204
Description
Right now it's hard-coded to 3 layers (fg, bg, and game layer). The backing data structures already support an arbitrary number of layers, but I haven't figured out a good way to do a UI to make it 'nice' as well as pretty on the code end.
We might eventually want to have more than the base 3 layers.
We would need:
- A way to add/remove layers
- A way to change the order of layers