Some tail fit improvements

Some changes to the tail fitting, mostly cosmetic regarding the output plots. Now the plots are divided by bin width to remove the spikey features resulting from the variable binning. Also plot axis labels have been added. The dividing by bin width makes real spikes more easily visible-for this reason I have changed the fit range (in doMSSM.py) for the ttbar emu nobtag template having spotted a spikey discontinuity at the point where the tail fit is merged with the lower part of the histogram. This was caused by fitting the tail from too low a mass point.