Updates relay board to versatile 32 relays board addressing 16 electrodes and 2 roles or 8 electrodes and 4 roles

Modifies schematics for scenario with single MN relays and analog multiplexers for roles M1 M2 and N. This assumes that the measurement board is modified to allow simultaneous measurements of M1 and M2 on the ADS, while N is put on the GND. The multiplexers would allow to cycle between a series of M1 and M2. See issue #60.

Adds draft kicad schematics for MUX boards for 8 electrodes with ABMN roles. It includes 4:1 multiplexing on M roles for multichannel acquisition.

Docs v2023

See merge request reversaal/OhmPi!14

add test_mux() to OhmPi and a bit of file tidying.

Closes #77

See merge request reversaal/OhmPi!13