Add "vibrate when silent" mode to notifications

* Add "vibrate when silent" choice in UI
* Add storage for it in Email's provider.  Existing accounts default to
  their current settings (always vibrate / never vibrate).
* Respect new mode when notifications are posted
* Updated existing unit tests

Bug: 2457183
Change-Id: I5c933ac39dbef8b2028255f330e0b084a445421a
1 file changed