a/ AliTRDCalibraFillHisto.cxx and .h: can set the range of the gain histo

a/ AliTRDCalibraFillHisto.cxx and .h: can set the range of the gain histo

b/ AliTRDCalibraVdriftLinearFit.cxx .h:
   can set the range and number of bins of the histos
   can add all histos together
   can see the fit (function public)

c/ AliTRDCalibTask.cxx .h: can set the range and number of bins of the histos

d/ AliTRDCalibraFit.cxx:
   No requirement of the three time but only two if we do not see the end of the signal

e/ AliTRDPreprocessorOffline.cxx .h:
   Can set the time constant shift due to the cut of the end of the signal before