Small fixes necessary

[liebermeister]

Hi Anne and Stéphane,

thanks a lot for your help!

I couldn't fix the "utf8" bug (which occurs when I use python 3.6), but I managed to install and run the pipeline with python 2.7 and 3.5. Now everyting works, including cplex.

However, on the way I had to fix two things:

o in setup.py I had to replace 'biopython' by 'biopython<=1.76'
(because the current biopython version requires python 3.6 or higher)

o in sbml_data.py, when using python3.5, I got many indentation errors.
I fixed them by replacing tabs by strings
of whitespaces. With python2.7, these errors did not occur.

Could you make the fixes in the repository? I will send you the corrected files by email.
Or should I send a pull request?

Thank you!

Best,
Wolf