Settings: New application-level notification settings.

 - Convert the old application-level dialog to an activity.
 - Move the settings icon to the new activity (out of the list).
 - Add a custom application header, similar to the switch bar style.
 - Use the ubiquitous vector gear for the settings icon.
 - Migrate old checkboxes to switch prefs, add new summaries.
 - Remove obsolete artifacts.

Bug:16396715
Change-Id: I857e3cf448b79f44fe1c242e6020f5214434c00c