R78 3state Checkboxes

Finally found use for so-called "3-state checkboxes" - the ones with "checked", "unchecked" and "indeterminate" states.

Basically, it's possible to control 2 bits (of related config data) as follows:

⦁ Unchecked state = both bits are off ⦁ Checked state = both bits are on ⦁ Intermediate state = one of the bits is on, another is off

I am not 100% sure if this will make it into the production version, but the idea looks useful.

Edit - here's a walk-through of the process behind this design - https://bvckup2.com/wip/22092017