Bubble settings: feature, notification, app

* Removed setting from developer options
* Removed bubble settings from normal notifications /
  channels

* Feature available via notification setting
* Feature screen with educational gif

* App level is now a tri-state choice of all / selected /
  none
* App level bubble controls are accessible top-level in
  app notifications

Test: make -j40 RunSettingsRoboTests ROBOTEST_FILTER="Bubble"
Bug: 138116133
Change-Id: Id103e9d3717fdc9b86a916be40c43cda9c35ac34