Activate the currently focused tap (only) on ambiguous auth events.

In the former behavior, two flows would be started (and both valves opened, if
present) whenever an ambiguous authentication event such as RFID swipe occurred.
Users have reported this as confusing, since after finishing the desired flow,
another flow will typically be dangling in the UI.

Solution for now is to only start a single flow; guess the desired flow based
on the currently-focused tap on the home screen.

This is probably good enough for >90th percentile use cases; most people
probably don't pour from two taps at once..
Add work-in-progress layout for CalibrationActivity (which also isn't done).

The Activity snuck in during the Service->Manager refactor.
It isn't yet exported / available.