Support different gamepad bindings

[avivace]

From this report on discord:

hey in the online gameboy emulator it uses X and Z for A & B buttons this is all fine on qwerty keyboard but not that good if you got AZERTY keyboards as we do here in belgium. as Z and W keys are swapped and this gives a weird position for the buttons. The fix could be rather easy (if it's possible) and it's to allow the W key (which on azerty keyboards sits next to the X key on the position where Z is on qwerty ) to be used for button B as well

We should allow the users to:

• Select between different presets for the gamepad bindings
• Create a custom preset (?)