Loading characters from map

Characters are now added directly into the tmx file, just create an object layer named characters and then you can add your characters.

To add a character you have to import it's sprite sheet as a tileset and use one of it's tiles to create an object.

When the map is loaded the character will have the same positon/orientation than the object from the map and it's skin will be found automatically.

The levels holy_grail, password, crepes and teleportation are updated to use this new method.