Secondary keybinds, new way of setting keybinds

[Stoppedpuma]

Allows the user to set secondary / alternative keybindings for actions.

Things mentioned in discussion with Woelper:

• Investigate recreating keybinding logic as notan may support (de)serialisation of input events.
• Look into refactoring existing implementation as a secondary option.

Extra support:

• Mapping mouse buttons (excluding M1 and M2)

New way of setting keybinds:

The keybind button should be pressed and set the key the user pressed. For modifiers, they are to be held and will be finalised when the user presses a non-modifier key.