Negative screen colors

**Is your feature request related to a problem? Please describe.**
When my pwnagotchi is running for over 10h straight then my screen slowly starts to fade to black and starts to show a huge trace where the previous face used to be. This might be caused by the fact that the e-ink display starts a bit of "burn-in".

**Describe the solution you'd like**
Since the default screen is black, I would propose to have a "negative" version of the pwnagotchi screen, where the background is black and the front is white. That way the pwnagotchi is better visible for those without good vision, and if you modify the screen you can turn it into a "color display".

**Describe alternatives you've considered**
Alternative for my problem is the "refresh" command that refreshes the full screen.

**Additional context**
No screenshots unfortunately... It's hard to show, but if you turn an e-ink display on for a long period of time, it starts to show "ghosting".

Start by locating the pwnagotchi screen-rendering code and the existing refresh command mentioned in the issue. Confirm how the e-ink display is updated and define done as an available negative screen mode that shows a black background with white foreground elements.

Written by the indexing model from the issue text.