Updated Controls

Due to persistent feedback about the controls being janky, in this version I've updated them to be more familiar - in addition to the WASD/Space/Shift control scheme, there is now also Arrow Keys/X/Z, which should hopefully feel more comfortable to use.

I've also slightly tweaked the way the UI for the pause/win/lose screens load, with the only real change being that the Next (for win screens) or Retry (for the loss screen) is selected by default, to make it easier to navigate by keyboard.