Resolve "Problems with current version of Celery (5.2.0)"

Closes #542

See merge request !849

Translations update from Weblate

See merge request !857

[Docs] Fix development documentation

See merge request !855

Resolve "Add recursive helper methods for Group"

Closes #408

See merge request !852

Currently translated at 100.0% (622 of 622 strings)

Translation: AlekSIS/AlekSIS-Core
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-core/de/

Currently translated at 100.0% (604 of 604 strings)

Translation: AlekSIS/AlekSIS-Core
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-core/de/

Update translation files

See merge request !856

Resolve "OAuth2 broken in 2.4"

Closes #592

See merge request !854

#592

Add trademark to readme

See merge request !853

Resolve "PDF files offered for download despite of error"

Closes #590

See merge request !848

Merge branch '470-login-with-local-django-accounts-and-ldap-password-changes-are-mutually-exclusive' into 'master'

Resolve "Login with local Django accounts and LDAP password changes are mutually exclusive"

Closes #470

See merge request !847

This is only set if LDAP is enabled on the site being migrated, to
ensure the change in 42f5708d does not
leave existing sites vulnerable to users authenticating with shadow
copies created before the change.

This fixes #470, where local Django accoutns were generally locked if
LDAP accoutns were used together with password handling to protect
against deleted/locked LDAP users being able to still login using a
shadow copy of their account in the Django database.

The fix introduces user account attributes, and the LDAP
authentication code keeps a record of users who used to authenticate
with LDAP in the past. If a suer is known to have been using LDAP in
the past, they are denied if they cannot be authenticated in the
future; if a user tries to authenticate who has not used LDAP in the
past, they are allowed in.

Resolve "AccountSignupForm accesses database on instantiation"

Closes #586

See merge request !846