Adding theme selector and workable light theme

[TheFreal]

Implements #31! Introduces #50, but that's not a blocking issue as it's quite the corner case.

QA checklist

• [x] Read state (state & power state)
• [x] Read primary battery SOC
• [x] Read primary battery cycles
• [x] Read secondary battery SOC
• [x] Read secondary battery cycles
• [x] Read seat closed
• [x] Read handlebar
• [x] Read AUX SOC
• [x] Read CBB SOC
• [x] Read CBB charging state
• [x] Update ping
• [x] SOCs are cached (after app restart)
• [x] Commands can be sent (locking & hibernation)