Added configurable game key bindings.
- Game keys (default Z/X) can be changed to any letter or digit in the options screen.

Other changes:
- Mouse/keyboard input in the "Game Paused Menu" state is now the same as in the game state (i.e. all game keys available).
- Moved 'isInputKeyPressed()' into "Utils" class ("Game" state didn't even call it).
- Trimmed 'failsound.wav'.

Signed-off-by: Jeffrey Han <itdelatrisu@gmail.com>