Added Dirac HNL proc_cards as well as potting script

[Nayaqs]

Added Dirac HNL proc_card, both for eenu and ejj final states.
Added a plotting script to select desired variables to plot, as well as a ReadMe to explain how it works.

[jalimena]

hi @Nayaqs ,

thanks for making this pull request. I think I can't accept this PR in its current form completely, but most parts of it are fine or just need simple tweaks.

Maybe first look here, particularly at the example where Mary develops a new feature:
https://www.atlassian.com/git/tutorials/making-a-pull-request

The main thing to learn here is that in general, you should make separate branches for each new feature you want to add.

You can also look at closed PRs from me to this fork, to give you an example of how it could look.

Then very practically, I would suggest a few things:

1. You make a new branch and corresponding PR for your madgraph cards you want to add. That is separate and easy to branch off.

2. You make another new branch and corresponding PR for everything in your plotting_tools/ directory. But also please change the name of the directory to something that makes it clear these plots are to directly compare Majorana and Dirac particles. If you're not comparing Majorana and Dirac particles, you probably want to use the more standard plotting tools.

3. Then you make a third new branch and PR for everything else. But notice:

• that some variables you want to add to analysis_final.py and analysis_stage1.py require an HNL input signal. However, the variables that are currently in those two files would also be fine for running over backgrounds as input. So, please duplicate analysis_final.py and analysis_stage1.py and call them analysis_final_HNL.py and analysis_stage1_HNL.py or whatever just somehow put HNL in the name of the file directly, and then add the HNL-specific variables in those files only. For the variables that also can be used for backgrounds, please add them to both copies of these two files.
• There are conflicts currently. Probably you have to pull the latest changes to this upstream fork in order to resolve these conflicts.
• also notice that you have committed changes where you undo things that have been implemented. Please don't commit these "removals" and correspondingly, don't hardcode your directories into what you commit to this common fork. Only you will write to your area, it is not applicable for anyone else. You can add, just please don't delete in this common area without good reason.

I might have more comments on this final PR you make, since that is the biggest one with the most changes.

So, I will close this PR soon and in the meantime encourage you to make 3 new ones. If you have questions, don't hesitate to ask.