Menu

Added an extra class Menu which allows you to open a menu screen. When
esc is pressed you now open a new screen that is slightly opaque and
colored black. This gives the impression of a menu. Very primitive
buttons, need to work on that, but you can resume the game and quit the
game from this menu. Should be noted that does not pause actual game at
the moment though not much is happening in the game so that is not the
problem. It simply refocuses you on another window, so no pause at the
moment but that can come in later by pausing the timer.