Modify AppHeaderController to provide UI for notif settings

- The AppHeaderController is no longer a singleton. Each time appheader
  should be updated we will create a new controller. It acts as a
  builder/mutator, user provides customizable inputs, and the controller
  will bind everything to UI when calling done().

Bug: 32442716
Test: RunSettingsRoboTests
Change-Id: Icfc5bcd8bc170a02b57432d864eaddf71db0d5b4