addPlotForFracChargeRelValMonitoring

Add two plots to the Tk DQM for the monitoring of frac. charged signal in relVals.
This changes were discussed at the PdmV/DQM Joint meeting of the 28th of october: https://indico.cern.ch/event/294179/

I have no idea...
You guys are the experts.
Last time I made a PR, I was strongly encourage to use the fillDescription method instead of the untracked parameters.  If you feel more confortable with the untracked I can use it.
Not being aware of all the python files loading this one, I am not sure it's a good idea to edit the python itself.
But I'll be happy to use whatever you suggest