[EHN] FD enhancements

[emanuelegiorgi]

Welcome to BioPAL, Yu!

@emanuelegiorgi and @francescobanda, list here a series of open points for FD code:

• tutorial preparation for current main change detection algorithm (see AGB Jupyter Notebook)
• improvement of documentation (docstrings in numpydoc style, variables naming, ...)
• add more testing (see ground cancellation test and FD test )
• support to new polarimetric algorithm see PR 33

These points can be a good starting point for you to get into BioPAL. Let us have your feedbacks!