Moving everything from MainController to Editor.
Fixing the MainController references in MainWindow.
Moving the on_undo and on_redo methods to the Editor class.
Fixing more broken references.
The layer surfaces now are managed by the new Tileset class.
Changing the palette loading process.
Adapting the tile selection feature to the latest changes.
A new Rect.normalize(). The old one is still being used but will be changed.
Comments and style changes in the tile palette.
Adapting the map render to the latest changes. The drawing tools are temporarily disabled.
Cleaning and removing the DrawingTools, the drawing feature must be created from scratch.
Removing unused stuff in enum.vala.
Fixing some scale references in MainWindow.
Changing some names in Tileset, and a new convenience method.
Removing the tools.
Changing more method names.
A new class, TiledDrawingArea, that inherits from Gtk.DrawingArea.
A new class, TiledMapDrawingArea, that inherits from TiledDrawingArea.

This is the new DrawingArea tree:
- Gtk.DrawingArea
  - TiledDrawingArea
    - TilePaletteDrawingArea (the tile palette)
    - TiledMapDrawingArea
      - MapDrawingArea (the map editor)
Some cleaning and changes in the DrawingAreas.
Removing unused stuff in the Tileset class.