Display: button backlight notifications follow pulse notification delay
ModPower: added option for proximity wake up (4.2+)
When enabled, device won't wake up in case prox sensor is covered
(prevents accidental wake up).
Feature introduces slight screen-on delay which is dependent on
proximity sensor (hardware) speed (only when feature is enabled, of course)

Revised by bgcngm
- Preference removed for Android 4.1
ModPower: optimized proximity wake up feature
Don't unregister sensor listener immediately but keep it running for
some time (MAX_PROXIMITY_TTL) keeping sensor state updated. This handles
situation when playful user keeps pressing power key repeatedly which
results in listener reg/unreg operation happening too fast in a row
which can sometimes confuse the sensor manager. We rather use current
sensor state coming from listener that's still alive instead of
registering a new listener.

Especially on Nexus 5, there seems to be some kind of a bug in sensor
HAL which can render prox sensor stuck in ON state forever, not sending
proper values at all (indicated in logcat as: W/qcom_sensors_hal(17970):
_hal_sensors_activate: Deactivating dirty sensor 31)
ModPower: use wake lock during proximity wake up
To give registered listener a chance to unregister in case device falls
back to sleep before listener TTL expires.