AGB estimation algorithm refactoring and re-organization to a more user-friendly and generic form

[imsoja]

[ENH+WIP] significant refactoring of the AGB estimation algorithm

• parameters, observables, formulas are not hard-coded anymore
• intermediate products are saved in a more readable form
• added flexibility to expand and choose the model

Tested and should be working fine Note: different model currently implemented to the previous version. The generated maps will look a bit different.

[emanuelegiorgi]

I and @francescobanda reviewed your request. New features and improvements are nice and welcome and pave the way for further enhancements. There is still some work to do to turn the code from this intermediate status to an APP:

• paths for new data, which are now hardcoded, shall be moved to configuration
• new parameter / observable properties shall be moved to configuration
• documentation shall be improved with docstrings
• some new features shall be added (as function for reading generic polygons, tables for management may be replaced by xarrays, ... ) All of this will be dealt with in the next step, however for the time being we verified that this PR is working and to be merged. Next time some more evidence would help the review (tests, plots).