Change battery monitoring to use upower

[Eeems]

Is your feature request related to a problem? Please describe.
Upower is the main standard for power monitoring on linux at this point. It would make sense to reuse that instead of maintaining custom logic.

Describe the solution you'd like
Use upower and expose the extra information this provides.

Describe alternatives you've considered
#280 is still useful for waiting for changes instead of scanning. Upower doesn't have a "changed" signal from what I can see.

Additional context
toltec-dev/toltec#786