Invisible by default, not activatable when the platform
volume controller is active.
However, when the platform volume controller is not active,
it can be enabled via a broadcast intent.
When enabled, the status bar icon also changes to a single
dnd icon.
Very little more than embedding the existing zen mode panel
into the detail pane of a new QS tile.
Change-Id: I1e0ff6fbb99b00f67b53bceda8cbf121f3ef6b52
3c4076a246