Read power bank SOC

[washed]

Maybe somewhat unnecessary, but i was thinking if we should read the power banks soc display to get this state into our application. This would allow us to do a few interesting things like

• warn when we are running out battery (playing a sound or something)
• performing a clean shutdown before the battery dies
• just do it because it's fancy

"worst case" would be to use a shift register to get the led states.

[tmh-alex]

[chimes, Majel Barrett's voice] Warning, core at 5 %. Emergency shutdown imminent.