Remove useless includes.
Fix custom entity sprite collisions with some entity types (#536).

Sprite collisions with switches were not notified.
Sprite collisions with crystals, fire and explosions were notified but
with a wrong order of sprite parameters passed to the callback.
Fix custom entity collision detection with entities not moving (#551).
Remove dead code.
Fix wrong comment.
Typo.
Editor: ensure that resource directories exists. fix #554.
Editor: authorize the / character in map ids.
Add a method sprite:get_animation_set_id(). Fix #552.
Add methods sprite:has_animation() and get_num_directions(). Fix #525.
Fix the write dir not having priority over the data dir since 1.1.
Editor: add a dialog to ask for create a non existing resource.