Separate character's logic in two classes

* Character model holds non-graphical logic
* DungeonLevelCharacterActor holds graphical logic
Separate dungeon level logic in two classes

* Dungeon::Level model holds non-graphical logic
* DungeonLevelActor holds graphical logic
Slap some Character specs
Merge pull request #59 from rafaelgonzalez/separate-backend-from-graphic-engine

Separate backend from graphic engine