BLN: Allow blink interval override

Currently the blink interval is determined by the current notification's params. Allow the user to override the intervals through sysfs.

EG:
    echo "700 3000" > /sys/class/misc/backlightnotification/override_blink_interval
This setting would luminate the lights for 700 msecs every 3 secs

    echo "" > /sys/class/misc/backlightnotification/override_blink_interval$
This setting will disable overriding and go back to regular intervals set by notifications.