Up+down and Left+right cancel each other out (closes #23 )
No longer allowed to bind the same keyboard/controller input to more than one GB input at once
Fix bug where all unbound inputs are registered as pressed when ´ is pressed on German keyboards (probably happens on other keys as well)
Warn user when they try to save inputs if SHIFT is selected (as it can lead to inputs being falsely registered as still held when SHIFT + a key that it modifies are used at the same time)
Allow configuring joystick deadzone threshold (between 25% and 75%)