Add centralised conftest

[atudor]

Background

Currently, sitescripts has one conftest.py file in the tests for sitescripts/extensions. This, however, prevents us from adding other conftest.py files when testing other modules.

What to change

In this environment, I suggest we create a dedicated conftest directory for the entire sitescripts, define specific fixtures for every module in separate files and then put them all together using the technique from here: ​https://gitlab.com/eyeo/websites/cms/blob/master/tests/conftest.py#L7

TO DO

1. Create a /conftest directory, with a conftest.py file inside
2. Move the contents of /sitescripts/extensions/test/conftest.py into a new file, /conftest/sitescripts/extensions.py
3. Add the fixtures from the new file in /conftest/conftest.py, using the techique linked above.
4. Add conftest at the head of the directories parsed by

[abpbot]

A commit referencing this issue has landed:
​Issue 7112 - Add centralised conftest