Lepton scale factors - final!!

Took several days to sort out this git mess, so please do check this looks ok to you.
I have made the corrections suggested by @kreczko in #123, which I have now closed.
I rebased, (eventually!) with upstream master and with @EmyrClement's hadronEfficiency branch so everything, including the commit history, should be correct and in order now.
If you do not have the private member variables any more, I would move these includes to Electron.cpp