Use short_title in compute_navigation

[jochenklar]

Shot titles where accidentally removed in RDMO 2.4.0. This restores there use in the sidebar of the interview. Draft for now since I don't know if we want to have an extra release for this.

[coveralls]

Coverage is 94.905% — 2.4.5/fix/navigation into 2.4.5/release. No base build found for 2.4.5/release.

[MyPyDavid]

I though it would be easy to add a simple test for this but I think that the TranslationMixin is broken somehow and we need to add a fix for that as well.

(Pdb)  django.utils.translation.get_language()
'en-us'
(Pdb) rdmo.core.utils.get_languages()
[('en', 'English', 'lang1'), ('de', 'German', 'lang2')]

and we try to compare 'en' == 'en-us'....

rdmo/rdmo/core/models.py

Line 38 in e77e2ca

if lang_code == current_language:

(Pdb) section.short_title_lang1
'SectionShorty'
(Pdb) section.short_title
''

🤯 ❓

[MyPyDavid]

Still the new tests (without the fix for TranslationMixin) did not fail in the CI somehow, maybe some leaky tests were setting the locale to en for the rest of the tests?! Because from the rdmo core default settings it should be set to LANGUAGE_CODE = 'en-us' ??
When the tests now pass than there was no problem at all (or something else is leaky) 😶‍🌫️

[MyPyDavid]

If these tests in #1590 also pass then I give up. 🎤-drop

[MyPyDavid]

Fixed and tested.

The two other changes to translations in the tests are unrelated but I don't want to force-push the branch right now so..

[MyPyDavid]

this was the test that was simply broken somehow on my machine because I had en-us as the locale language