Settings: Battery saver updates.

 - Fewer trigger level options, new default of 0 (never)
 - Use new shared feature description text (in framework)
 - Remove "always on", add new top-level switch bar.

Depends on the framework changes in I3d1ded1eec9e63e7d97469486f6a320e1bebbccd

Bug:16214395
Change-Id: Ia01186cfeb19d00672f62cc84787584b4dcc1143