Missing dependency in 4.2.9

Description

sphinx is not in requirements but is imported by pywps.test.

This does not seem to be a problem in master, but not sure if it because the issue was fixed, or the commit not pulled into master.

Steps to Reproduce

conda create -n pywps4.2.9 python=3.7
conda activate pywps4.2.9
python setup.py develop
python

Then

from pywps import tests
Python 3.7.9 | packaged by conda-forge | (default, Dec  9 2020, 21:08:20) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from pywps import tests
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/david/src/pywps/pywps/tests.py", line 15, in <module>
    from pywps.ext_autodoc import MetadataUrl
  File "/home/david/src/pywps/pywps/ext_autodoc.py", line 2, in <module>
    from sphinx.ext.autodoc import ClassDocumenter, bool_option
ModuleNotFoundError: No module named 'sphinx'






# Additional Information

Sphinx is in

pywps/requirements-dev.txt

Line 4 in 20e1e25

Sphinx

so that might explain why it's passing on Travis-CI https://travis-ci.org/github/geopython/pywps/builds/750280910

That's coming from my commit 2a55b6e, so should I have created the MetadataUrl class in pywps.app.Common instead?

I introduced the commit above in this PR #542. It was my first time touching pywps code. The class MetadataUrl should probably be in pywps.app.Common together with Metadata instead. Will submit a PR for this.

fixed by PR #565