Add a script to generate material scan plots

[Chao1009]

Briefly, what does this PR introduce?

Add a script to plot the scan results from "bin/g4MaterialScan_to_csv"

What kind of change does this PR introduce?

• Bug fix (issue #__)
• New feature (issue #__)
• Documentation update
• Other: __

Please check if this PR fulfills the following:

• Tests for the changes have been added
• Documentation has been added / updated
• Changes have been communicated to collaborators

Does this PR introduce breaking changes? What changes might users need to make to their code?

No, it's a tool

Does this PR change default behavior?

No

[Chao1009]

Some use cases:
Generate material scan data:
>./bin/g4MaterialScan_to_csv -c $DETECTOR_PATH/epic_craterlake.xml --eta-values="-2.5,0.,2.5" --phi-values="0." --raw-output
By enabling the flag --raw-output, you will get multiple data tables with the file name "scan_raw_....csv".
Make the plots:
>./bin/g4MaterialScan_raw_plot scan_raw_eta\=0_phi\=0.csv --path-lengths="0, 80, 300"
>./bin/g4MaterialScan_raw_plot scan_raw_eta\=2.5_phi\=0.csv --path-lengths="0, 340, 600"
>./bin/g4MaterialScan_raw_plot scan_raw_eta\=-2.5_phi\=0.csv --path-lengths="0, 180, 600"
Here the number of path lengths defines the number of subplots (N-1), and the values will be used as the x ranges of the subplots. For example: "0, 80, 300" gives two subplots with path lengths within [0, 80] and [80, 300].

[Chao1009]

Plot examples:

[Chao1009]

The next step would be adding annotations for detectors (path length ranges), and we will do it in a separate PR because it will be more complicated if we want to determine the ranges automatically and precisely. One can still manually add the annotations with the plots generated from the current scripts.
The PR is ready to be reviewed and then merged.

[torrijeske]

units on plot should be cm and not mm

[veprbl]

Following discussion in VWG meeting today, let's merge.