PCB design

[daviderovell0]

Merge the control and audio breakout boards and expand the for the new features.

New components

• [x] +1 MCP3008 ADC for the CVs and CLK. see #53
• [x] Header for RPI4
• [x] Screen: choose model, components to drive it?
• [x] 4 buttons

Requirements

• Make it as HAT for the Pi
• Conform to JLCPCB board design rules
• Components should be available from JLCPCB to exploit their SMT soldering