- Simplified the fast discharge circuit to use a single PNP BJT instead
of two NPN BJTs
- Swapped nRF52 module's footprint for one with larger pads
- Added a user button tied to P0.12 (same as Button 2 from [nrf52840_dk](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fug_nrf52840_dk%2FUG%2Fdk%2Fhw_buttons_leds.html))
- Added a reset switch
These are only schematic changes - PCB layout is stale and needs to be
recreated.
