- Move most properties from TileMap to TileSet,
- Make TileSet more flexible, supporting more feature (several
collision layers, etc...),
- Fusion both the TileMap and TileSet editor,
- Implement TileSetSources, and thus a new way to index tiles in the TileSet,
- Rework the TileSet and TileMap editors completely,
- Implement an editor zoom widget (and use it in several places)
