Python and C++ code refactoring

[carloslihu]

• Python code is now formatted with black and isort, and has been refactored according to PEP 8 style guides.
• Python code partially commented with google docstring format.
• C++ code partially commented with doxygen docstring format.
• Scott's and Normal Reference Rule's bandwidth calculation have been reordered and commented.
• ArcOperatorSet::update_incoming_arcs_scores formulas have been reordered and commented.