Show snoozed conversations in conversation header

- And allow them to be unsnoozed with a tap.
- Also use the conversation's shortcut icon and name if available.
- And ignore the setting to turn off the strips since it now requires
explicit user action to make the strip visible

Note 1: unsnoozing a notification causes it to make sound again - we
probably want to change that for manually unsnoozed things
Note 2: the entries in the header don't yet persist across a reboot

Test: atest, manual
Bug: 149486431
Change-Id: Id661c25a49bc982e39deab977eb912f51eaf6757