computeSsFlags: now return pair<DilepVars, SsPassFlags>

Details:
This avoids hiding the DilepVars inside computeSsFlags, and having
to re-compute it in other places.
- define std::pair<susy::wh::kin::DilepVars, SsPassFlags> and create dict
- typedef VarFlag_t
- modify calls to computeSsFlags
typo: rename HtfFiller.* HftFiller.*
..
MatrixPrediction: note to self (possible bug?)
add --with-hft option
HftFiller : move some pars to init (not available at construction time); call WriteTree
SusyPlotter: instanciate and use HftFiller

Details:
several changes, start using HftFiller.
- add m_hftFiller
- Implement and used new methods initHftFiller, fillHft,
  closeHftFiller, toggleHistFitterTrees
assign remaining variables; requires HistFitterTree-00-00-31