Attached patch moves "default" from 3.6 to 3.9

Additional changes:
  Remove 3.5 from all
  Change future to 3.10


Other point:

As 3.5 was never reall deployed, I think we can remove it from the 
distibution.

As we have a lot of python3-* is obsoleded py python36-*
what is the best way to updated to python39-* when available ?

Regards
Marco