Lepton scale factors

This is the (mostly) finished update to read 7TeV electron scale factors from histogram files.
Compiles and runs, but during running there are some warnings of memory leaks related to TEfficiency, which I was unable to solve...hence WIP.
Also, will remove the couts once this is ready to merge.
while this is OK, I would add a comment to make clear that our selection requires >= 4 jets.