Battery: Show battery fully charged notification

This feature is device configurable using config_showBatteryFullyChargedNotification.
When enabled the BatteryService will show a notification informing the user that the
battery is fully charged and that they should disconnect the device from the charger
to improve battery longevity (citation needed) ;)

Change-Id: I9214c880705c58b67b422fbf3977913e93a0a737
TICKET: PAELLA-91