Update Python and Django version metadata

[Flimm]

Correct setup.py and README.rst to match the supported versions.

[codecov]

Codecov Report

Merging #689 (ac41718) into master (de96f2b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #689   +/-   ##
=======================================
  Coverage   73.70%   73.70%           
=======================================
  Files          30       30           
  Lines        1700     1700           
=======================================
  Hits         1253     1253           
  Misses        447      447           

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[claudep]

Thanks for the PR. What about also setting Development Status to Production/Stable, as suggested by Uri (#683 (comment))

[camilonova]

@claudep can you do it on a separate PR?

[claudep]

Sure, will do!