Minor refactoring

Added nPixelMatch histograms (currently not functional and being
debugged.)
Refactored the plotting code into a single block instead of two almost
identical blocks.
Only plotting variables for the “best” helix.
Added protection to ensure histograms are always plotted, even when
they are empty.
Added protection to set efficiency to 0 in case of there being no
electrons in the denominator.
Bugfix

Fixed typo in a file name.