Moving to a python3-compatible code

Ensuring python3-compatible code, while keeping python2 compatibility. The code was tested with both python 2.7 and 3.9 (including on HTCondor).

In particular:

• calls to print modified (parentheses added, removing print >> for prints to file),
• time.clock() -> time.time()
• np.int(...) -> int(...)
• // instead of / for integer division,
• removing split and replace functions from string module (using corresponding methods from str objects instead),
• list added whenever needed (with e.g. range, items(), map),
• all semi-colons ; removed,
• using npz format for saving pickles and numpy arrays, and various options changed there,
• handling of HTCondor batch job modified, and DELPHI_script.py as well.

There were also a few additional changes:

• a test script for noise (eta) calculation was added (with comparison with an approximated approach) in DELPHI_Python/test_scripts/test_noise.py . This replaces the one that was directly in DELPHI_Python/Noise.py, now removed (to avoid useless matplotlib imports when launching DELPHI calculations),
• an old test script with various outdated tunespread claculations was removed in DELPHI_Python/test_scripts/,
• the README.txt in DELPHI_Python/test_scripts/ has been changed accordingly,
• clean-up of the LHC example script.