Code reorganization

[lucalavezzo]

• [x] Move ML to additional_tools
• [x] Move Dask to additional_tools
• [x] Move unit_tests to additional_tools
• [x] Add Contributing.md and describe unit_tests
• [x] Split plotting/ in histmaker/ and plotting/
• [x] Change imports accordingly
• [x] Rename setup.sh to shortcuts.sh
• [x] Rename condor_SUEP_WS.py to condor_SUEP_ggF.py, adjust kraken_run.py accordingly
• [x] Change READMEs accordingly
• [x] Remove replace_in_file.ipynb, move_merged.ipynb

[lucalavezzo]

I tested submit.py, kraken_run.py, condorSUEP*.py, ran the unit tests, make_hists.py, and plot_utils.py, but I do expect some path/import error coming up...

[lucalavezzo]

Resolved in #287