First version of Gigas, animations are OK.

Todo :
* Remake the room to have only low layer, like first version of the map
* ATTACKS
  * Spirit balls split : six balls going random for random time and going
together again
  * Poison Gaz
  * Invoke Lizalfos : random apparition of lizalfos in the map (check for
obstacle first
  * Create thunder attack : make a generic enemy "lightning" with possible
step, and stop when hurt hero or touch obstacles
Enhancement of Gigas

* New room for the fight
* Fix multiple arrow shoot by setting invincibility when transforming
* Better size of the enemy
* Better placement of origin point on the hands_down animation