RECONSIDER: Editor: Allow selecting and positionning masked textures

Be capable o define what will be the masked textures in the palette and how should those texture be positioned in the maze.

Indirectly, it also means improving the preview in the top right corner of the editor by reusing the maze engine drawing functions but by shrinking the values by 1/4 to 1/8 of the original size. Not sure if possible.

UPDATE: In order to simplify development for emergency only, it could be possible to use a single masked rectangle texture for all events. Then have quick keys that will put the default masked texture at the right place. That prevent the need to select a masked texture.

UPDATE (08-2022): Not sure if masked texture overlay would still be a thing. The engine will massively reduce the number of custom masked texture since it's focussing more on function than look: Door, grid, decoration, etc.

TODO: If still a necessary feature, will have to be moved into the Mapper project.