recovery_ui: Add support for battery capacity status

This is a reworked version from the older GUI
implementation (I89c963e75bbc40f4bb7204211773fbfb28a5206b).

- Update for the current recovery/fastbootd UI
- Use loop to update battery capacity in background
- Reflect charging status by appending "+"

Change-Id: If7a6c080da273dfedddffcbea5e0ce12e677bf2f
Signed-off-by: Chippa-a <bagirovvusal99@gmail.com>