utils : enumFromHeader
working implementation; validated against c++ code

Details:
This implementation produces the same weighted matrices as done with
FinalNewFake. The file is self-contained, but it parses the
SelectionRegion enum to understand what are the signal regions for
which we should produce the matrix. Perhaps this could be improved and
guessed from the input root files.
Caveats:
- the scale factors (coming from the iterative procedure +
  FakePlotting) are currently specified in the code (was already like
  that, but it should be improved)
- almost all of the output histograms match exactly the ones produced
  by FinalNewFake. There are a few exceptions for the mu fake rate:
  CRZVMet, CRZVMet, CRZVmT2_(100,120,150). These are due to the fact
  that I do not consider the conversion histograms for muons. In these
  control regions, there are about 10% of the fake muons that are
  classified as 'conversion'. The resulting p(T|F) is about 10%
  larger.