Support multi-joystick prioritisation

[ES-Alexander]

• show as tabs on the side
• allow dragging joysticks to prioritise
  • by default only the top priority joystick has MANUAL_CONTROL outputs enabled
    • see #615 for some context
  • if multiple joysticks enable MANUAL_CONTROL, outputs are determined based on prioritisation (e.g. both can press buttons, and control axes, but if one they're fighting over the state of a particular button function or axis then the higher priority one wins)
• if keyboard and mouse support are added, they could be considered as alternative joysticks, subject to the same prioritisation/mixing (we could rename the section to Control Input Devices or similar)
• one input device could conceivably activate a modifier function to affect the outputs of another input device, if it is configured to have control over a modifier function that the other device uses
  • this would allow a 'teacher' to have a physical switch on their controller that disables input from a 'student'
  • provides more native input mixing/sharing/coordination options