Create shell UI for smart battery saver

This CL creates the new screen WITHOUT any of the behaviors
(changing the global settings/calling power manager apis) and
hooks it up to the preference in BatterySaverSettings for
navigation. The logic for the preference in BatterySaver Settings
is also added so that it shows the correct summary when the
schedule settings are modified. Additionally, a small tweak is
made to the radio preference widget to make it possible to hide
the appendix view. It didn't seem to do anything except get in
the way and potentially ruin your day, much like its biological
counterpart.

Test: Overriding power mode via adb, robotests
Bug: 111450127
Change-Id: Ic681aaf565ce1caf7d00d314e14ae6c4779fe8f6