[tox] Have less test environments This is to reduce the load on CI server because of parallel clones of the repository in Docker containers. Only keep "server", and "web" environments separated. All other prior environments are in "misc". To avoid duplicate entries in requirements files, move them all in a "requirements" directory (this appears to be a "common" practice, see e.g. Celery). Adjustments in tests: * Rename cubicweb/hooks/test/unittest_notification.py so that it does not conflict with cubicweb/sobjects/test/unittest_notification.py during test discovery as they would have the same module name but different __file__ attribute. * Add "comment" cube to the list of expected cubes in unittest_cwconfig.py as this cube is pulled by requirements/test-mist.txt. Closes #15440662.

CSS Coding Standards
--------------------

(Draft, to be continued)

:Naming: camelCase

Indentation rules
~~~~~~~~~~~~~~~~~
- 2 espaces avant les propriétés

- pas d'espace avant les ":", un espace après

- 1 seul espace entre les différentes valeurs pour une même propriété


Documentation
~~~~~~~~~~~~~
Please keep rules semantically linked grouped together, with a comment about
what they are for.

Recommendation
~~~~~~~~~~~~~~
- Try to use existing classes rather than introduce new ones

- Keep things as simple as possible while in the framework

- Think about later customization by application

- Avoid introducing a new CSS file for a few lines of CSS, at least while the
  framework doesn't include packing functionalities