Towards more complete RelVal

* previous functionality of comparing 2 files as usual
  --> whenever user-specific comparisons are needed, 2 corresponding
     files with histograms should be created and passed to the wrapper

Major developments of python wrapper

* include and steer all RelVals via python wrapper

* derive histograms from Kine, TPC tracks and Hit TTrees and perform
  RelVal on them
  In these cases, 1D histograms are simply extracted for all possible
  TLeafs using TTree::Draw. It is made sure that the created histograms
  have the same binning and ranges to be comparable

* QC now also part of it

* enable single RelVal with
  --with-<which>
  where <which> is one of
  analysis, qc, kine, hits, tpctracks
  These options can be combined arbitrarily.
  If none is given, run all of them

* most plots can be disabled passing --no-plots

* for more info see header of the file or run with --help

RelVal C macro devs

* add more ratio plots and fit linear function the ratio which is
  expected to have a constant value around 1 and vanishing linear
  coefficients
  * implemented for 1D
  * 2D (and potentially 3D) to be added

* fixing problems when MonitorObject or histogram in initial ROOT files
  has a "/" contained in its name

* now mark as "non-comparable" when 2 corresponding histograms are empty
  (previously it was narked as "not passed")

* apply O2 clang format

Author: Benedikt Volkel