Amiga configuration preference panel

[borb]

Not yet sure if this makes sense if using i²c display (issue #5) and runtime configuration via keyboard hotkey (issue #6).

Gist is, button 1/2/3 are bidirectional pins on the Amiga side (they do go through a 74LS157 two-to-one line multiplexer), but can be used for bidirectional communication. Would need some form of attention-signal detection before beginning communication.