Add option to disable automatic flow start.
flow activation: Activate on all unmanaged taps during ambiguous auth.
CoreActivity: keep screen on for all activities.
FlowManager: add convenience method to get all active taps.
PourInProgressActivity: enhancements to multi-tap pours.

- Only show active taps when the activity is started. Closes #15.
- When multiple pours are active and one is ended, auto scroll to
  the next active pour.
- Grey out buttons when pour is ended.
SetupActivity: move cancellation.