Selector: m_signalJets2Lep -> m_signalJets

This is what Suneet is using; not sure it's the correct one
add 2 signal lep flag+counter (eq2slep)
plot_emu: add symmetric selections
rewrite CutFlowCounter

pass the cut string when incrementing, not at initialization.
This ensures that we're increasing the right counter (otherwise
there's the risk that the increment is off-sync with the list
of counters that was passed to the constructor).
Selector: move eq2sl after mll (same as Suneet)
CutFlowCounter: summary, print index (ease comparison)
DileptonVariables: add ncljets, nfj, nbj, ntau
lep eta<2.4; incrementObjectCounters returns bool