Refactoring and adding graphics

[GuillemBarroso]

Massive change in the game implementation. Now using sprites to determine collisions, improved map graphics and sound effects.

These changes were made to the screen window, and not the command line. A few things have to be done:

• Integrate the already implemented CL functionalities in the new game implementation.
• Allow the player to face in a 45 degrees angle (NE, NW, SE, SW).
• Remove certain UI implementation, such as displaying the player stats, and create a command to display it in the CL.
• Allow the player to move to a different room. Ideally, having an open map with several rooms/caves/houses around the map.