*WIP* Do not merge: Rotation

This recognises the rotation of tiles and resets the GID. I'm not too sure if I've hit every use case here. I haven't tested the flip horizontally and vertically tiles yet, I'll do that later. Also, I think it will require some kind of array to keep track of which tiles are flipped, and in what way. Any input you have about where this can fit in to the interface would be gratefully accepted.