Only make one call to get mouse position and get rid of the sf::RenderWindow parameter in Level constructor because it was only used to call LoadMap which we can do perfectly fine when initializing the class.
Load the menu level from a separate thread and fix a crash when loading Levels/level2.txt (had no player defined).
Implement a proper loading bar based on the amount of tiles left to be loaded. Also for now disable sound by default in Game constructor because it's annoying.