Adapt names of multiplicity histograms in EventLoader type modules
Plots of the number of pixels per
Corryvreckan event are named in most event loader type modules as
pixelsPerFrame, but the title of the histogram is "Pixel multiplicity per Corry frame". This could be unified.
My idea is to title these histograms as "Pixel multiplicity per Corry event", and name these histograms in the code and ROOT file as