Change battery monitoring to use upower

**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**
https://github.com/toltec-dev/toltec/pull/786