Somewhat inspired by change committed by Gavin Ni gisngy@gmail.com
back in cm-13.0 days (see commit 88e7a6c). Since then completely
rewritten using BluetoothDevice API introduced in Oreo, with new
drawables meant to be used with 0-9 battery level range.
Change-Id: I6179bfd41e033591534e8cf3c6adc98ce715a13d