Improve analysis3d tutorial notebook #1884
Continuing pull request #1860 ...
As suggested, I left this notebook with the original dataset (no need of CTADATA, FERMI or GAMMAPY_EXTRA anymore) but including the part of the galactic diffuse emission subtraction. I also attached the static image at the end of the notebook, as well as the path to access the complete notebook already submitted into GAMMAPY-EXTRA.
P.S. The previous branch was "too old" and to avoid conflicts with some functions that were modified I created a new branch... I tried to keep everything in the same commit but apparently I failed! apologies, next time I will try with