tmva: truth matching for signal efficiencies
tmva: remove spectator truth variable

Since only MC samples have truth variables, this fails when one of the
training samples is data.  Implement truth matching some other way.
tmva: efficiency scans for different MVA classifiers
tmva: rewrite efficiency scan script

- Rewrite script to add truth matching for signal selection efficiency
- Above only works when plotting from a normal ntuple (not TMVA output)
  1. apply MVA on ntuple
  2. plot from output of step (1)
- Also add documentation and other cleanups
tmva: minor conf cleanup
tmva: provide dummy methods on import failure
tmva: add checks to efficiency scan script