Add service to get persistent charger error log.

[cburbridge]

This adds a new service to the scitos node: /charger/save_persistent_errors. This service takes a std::string filename as the parameter, and saves the robots internal error log to that file using the MIRA service savePersistentErrors. Usage:

strands@betty:~$ rosservice call /charger/save_persistent_errors "filename: '/tmp/errors.txt'" 

example output:

[
    {
        "Accu24VVoltage" : 22.57400131225586,
        "AccuCurrent" : 1.876000046730042,
        "AccuCurrentExternalCharger" : 0.0,
        "AccuCurrentInternalCharger" : 0.0,
        "AccuLoadVoltage" : 22.24200057983398,
        "AccuMaxCurrent" : 1.896000146865845,
        "AccuMinVoltage" : 22.06600189208984,
        "AccuStatus" : 2,
        "AccuVoltageExternalCharger" : 3.105000257492065,
        "AccuVoltageInternalCharger" : 0.004000000189989805,
        "CellVoltage" : [ 2.94100022315979, 2.928000211715698, 2.722000122070312, 2.776000022888184, 3.049000263214111, 2.790000200271606, 2.872000217437744, 2.496000051498413 ],
        "Code" : 16843011,
        "CurrentVelocity" : {
            "Phi" : 0.0,
            "X" : 0.0,
            "Y" : 0.0
        },
        "CurrentVelocityTime" : 56532,
        "EmbeddedPCStatus" : 15,
        "EmergencyCode" : 36864,
        "ErrorRegister" : 128,
        "GlobalCounter" : 15195350,
        "Message" : "Cell undervoltage",
        "NodeID" : 1,
        "PowerupCounter" : 5,
        "RequestedVelocity" : {
            "Phi" : 0.0,
            "X" : 0.0,
            "Y" : 0.0
        },
        "RequestedVelocityTime" : 35535,
        "Type" : 1,
        "UnixTime" : 1422172242000000000
    },
   ....

These error logs are often requested by MetraLabs, so this just avoids the need to stop the robot and run miracenter manually.

[marc-hanheide]

retest this please