Allow setting a per-device default configuration for STATUS_BAR_BATTERY

Batteryless devices (like TV-connected mediacenters/STBs) don't need
the battery icon there at all.

Change-Id: Iac7e1b0b813c260bc78f4733409a30da7bda248d
Merge remote-tracking branch 'cm/cm-10.1' into cm-10.1-linaro