arcade-panel: start on hinge, better panel layout

arcade-panel: start on hinge, better panel layout

Half of one half of the hinge, and an attempt to make better use of
the attach() module.

Move closer to a workable panel layout: fix button hole sizes, lower
buttons vs joystick (seems to be a common design decision for compact
control panels), and switch the 1P start / coin buttons to 16mm round
switches to save space.

Hinge uses OpenSCAD Joint Connectors v1.0 by MakerBlock
<www.thingiverse.com/thing:33426> CC BY, source included for
convenience / possible local changes.