Added battery charging and battery state ROS interface

The battery sensor now detects whether it is in a certain range of a charging zone (default: 0.5 meter). A charging zone can be any object in the simulation with an object property 'ChargingZone'. This property can be added as follows (builder script): 

        myobject.properties(ChargingZone = True)

whereby _myobject_ can be any type of object. 

The ROS msg published by the battery sensor is of  type scitos_msgs/BatteryState:

        std_msgs/Header header
          uint32 seq
          time stamp
          string frame_id
        float32 voltage
        float32 current
        int8 lifePercent
        int16 lifeTime
        bool charging
        bool powerSupplyPresent
        float32[] cellVoltage

Currently only _lifePercent_ and the _charging_ flag are reported.