Configurable button actions

Right now, the system button controls the manual-0%/manual-100%/auto state of PWM. This is good for a Solanera which actually controls an appliance.

There is a use case for switching on/off the screens: both the OLED screen and the TM1637 displays. This is good for a Solanera which only acts as a display.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information