Run Galsim_Hub model in tensorflow 2.0

[ismael-mendoza]

It appears that having tensorflow 1.0 as a dependency keeps giving us security warnings and comes with other problems (like compatibility with other newer packages). It would be nice if we could migrate the galsim_hub model to tensorflow 2.0 somehow - I think @aboucaud , @thuiop had some ideas?

[aboucaud]

I'll propose something indeed.

[ismael-mendoza]

Deprecated for a while, please feel free to repoen if this becomes of interest again