Started on tha ctual graphical theme, 'dungeon'.
Improved wall image. Still very basic at the moment.
Added doors to the dungeon! They block movement until the player
interacts with them (by bumping).
Can no longer see through doors, and renamed interaction method so it
makes more sense.
Every move the player makes now takes time. However, now certain doors
never change to appear open.
Adjusted World to always have a reference to the Game. Player now calls
a dummy PlayWorld.lose() method when it dies.