Clean up ZFinderPlotter

Change variables names to be more consistent.

Change define guards to include the project name.

Where possible move includes into the cc file.
Add a PDGID enum

This enum maps PDG ID values to (more) sensible names.
Clean up ZFinderElectron

Change variables names to be more consistent.

Change define guards to include the project name.

Where possible move includes into the cc file.

Now using PDGID enum for particle identification.