Separate notification area into own controller.

Extracts the notification area of the status bar into a layout file and
create a NotificationAreaController that controls what happens in this
area.

This is to allow this area to be configurable in Android Auto Embedded
cases where OEMs may want their own custom implementations here.

Change-Id: I8a52af676d16fd6f7d3878805970a5897d2db945