Introduce quiet mode state to managed profile users

Quiet mode means the user will be free from visual and audio interruptions
from apps inside the managed profile, including notifications, widgets and
others. This CL adds the underlying state bit to users and exposes various
APIs to control and query the quiet mode state.

Bug: 22541941
Change-Id: If5f8e5a897843050e83b6ec26cb39561098f12b9