Implement Tiling

[Goobo-Studios]

Upon closer introspection, I believe tiling would be a much more difficult task to grid snapping. So i'll just write it as a seperate issue

[sci-comp]

Tiling is a great idea, its a feature present in most level design tools that I've seen.

You're right, this might be best done after grid snapping since the user might like to snap tiled instances to the existing grid.