Input button bindings

[Twisol]

Quoting Jorenz from #88:

• Enter should probably be allowed to select menu items as well
• The left thumbstick should be allowed to act as up/down/left/right
• Why is Y used to continue to the simulation phase? (should be A)

[Twisol]

• Enter now works for menu navigation.
• The left thumbstick is now bound to the pointer, rather than the directional keys.
• Y is used because A is bound to Select (i.e. click), which makes it intuitive for picking up pieces. B is used for removing pieces, and X is used for opening the toolbox. The only one left is Y (and personally, it feels pretty good there).