Create Beamline benchmark (#154)

Adds a first round of electron beamline benchmarks which demonstrate the path taken by the electron beam through the outgoing beamline magnets.

Plots show the position and shape of the beamspot, correlation between position and momentum. The position, rotation and radius of the detector planes is also output.

Co-authored-by: Dmitry Kalinkin <dmitry.kalinkin@gmail.com>