compute_fake_compositions: also mu, also plot vs mt, add pt>20 req
compute_fake_el_scale_factor: split output in subdirs, add pt>20 req
drop compute_lepton_efficiency.py

this was just an initial test; now superseded by compute_eff_from_ntuple.py
rootUtils.fetchObjectsFromFile minor improvements

return a default empty object when cannot open the file.
improve verbose messages
fakeUtils.plot2dEfficiencies: add textFormat

sometimes I want to plot more digits for easier comparison
also determine the efficiencies for all samples together

this will be used to estimate the error on the composition.
compute_fake_compositions: drop bb/cc for electron
compute_fake_el_scale_factor minor bugdfix (ext -> .ext)
compute weighted average from nutples also for muon

This required also a few changes in compute_fake_el_scale_factor
and in some util functions in buildWeightedMatrix. Note that
buildWeightedMatrix will become obsolete, so these functions
should be moved to some other module
build_fake_matrices: separate output files el/mu