refactor: Hoist all rpc calls to `ActivitiesScreen`
Components are more reusable when they have minimal state
and/or dependency on outside resources.
This commit raises the rpc calls to `ActivitiesScreen` which has
the responsibility for managing the data flow and interactions
between components.
This update also fixes a few bugs:
- Tapping an activity chip will start the activity if it doesn't have
any tags.
- The switches now update automatically after an activity is started or
stopped.
closes thehale/SimpleTimeTracker-WearOS#12
closes thehale/SimpleTimeTracker-WearOS#13