battery saver mode: a bit of a revamp

credits to Yanuar Harry
<ai.the.smarties.physics@gmail.com>

Change-Id: I22e45d652a1823698927d72f88daa9ad8bf55737
Signed-off-by: Dan Trifan <jimsth@gmail.com>

Conflicts:
	packages/SystemUI/res/values/pac_strings.xml