Added Power Brick related battery_status.msg fields

   system_source - This battery status is for the brick that is
                   supplying VDD_5V_IN
   priority      - Zero based, This battery status is for the brick
                   that is connected to the Power controller's
                   N-1 priority input. V1..VN. 0 would normally be
                   Brick1, 1 for Brick2 etc

  Battery now assigns connected from the api in the
  updateBatteryStatus, as well as system_source and priority