Editor: Support multiple autotilesets per tile

[Vankata453]

Tiles can now be present in multiple autotilesets in the same tileset. They would be autotileable with all (max. 10) autotilesets they are included in.

The editor allows for pressing keys 0-9 to choose from all 10 autotilesets the user can tile with. This is visually indicated in the autotile help strings.