Level selector was already working after work by William but some small bugs remained to be fixed + it wasn't possible to return to level selector once we were in the level.
- it's now possible to go back to level selector from Level
- LevelManagerScript is no longer a singleton (this way, it resets with the Game scene unloading)
- Added a property drawer for using scene files in inspectors
- Régler le problème où les icônes sur la carte ne s'affichait pas correctement;
- Ajout d'une condition pour empêcher l'utilisateur de selectionner un s'il est vérouillé.
