- Reports the current status of the battery (discharging, charging, full).
- Also notify the upower daemon when there is a change in the battery
  value.
- keep the battery value as a percentage, not the raw value
- add WACOM_QUIRK_BATTERY to easily add a battery to a device (required
  for Bluetooth devices)
Signed-off-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Acked-by: NPrzemo Firszt <przemo@firszt.eu>
Acked-by: NPing Cheng <pingc@wacom.com>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>