Added 2012 btag SFs and changed eventcount analyser

Added 2012 btag SFs. Still using last years B tag efficiencies as these were not on the twiki for 2012.

Event count analyser now reads in the btag weights so that the numbers are more consistent between the numbers here and the in the histograms.
Now the number of events in the cut flow table for >=4 jets = the sum of all the different _btag bins in the histogram. There is still a slight discrepancy between number of events for the >=2btags cut in the cut flow and the sum(_2btags, _3btags, _4orMoreBtags) in the histograms. Not sure what is causing this as the weights for the 2 are now exactly the same. Probably something to do with the histogram helper that i still don't quite fully understand.