Display: added option for emulated battery charging light
Existing "Disable charging LED" option replaced with "Battery charging
LED" which supports:
- default charging light (as comes with the rom)
- emulated: for devices that lack native charging light support (e.g.
Nexus 5)
- disabled charging light

Emulated mode uses notification light taking into account whether
there's a pending notification which user should be notified of. Pending
notification light has priority over battery light which means when
notification which uses led arrives, charging light is interupted in
favor of notification light. Charging light returns after pending
notification light is dismissed.

On devices with RGB LED hardware, charging light will lineary change
color hue from red to green according to current battery level (similar
way as lockscreen battery arc does).