tmvaconfig: fix printing
classify.py: mandatory session and output file
tmvaconfig: signal/bkg file and tree name in conf

In TChain format
classify.py: signal/bkg file and tree name (cli & conf)
tmvaconfig: minor change
Trivial clean-up
tmvaconfig: minor parsing fix (cuts & conf docs)
tmvaconfig: new property cut_both for common cuts
tmvaconfig: ensure cut_* always return a TCut obj
TMVA.conf: first dsk training config (name: base)