Add check for loading data to ClassLoader instances. Fixes: #12135

[SukiCZ]

Proposed changes

This adds a deploy check (python manage.py check --deploy) that will check all instances of ClassLoader and tries to load their data.

Fixes: #12135

Checklist

• Lint and unit tests pass locally with my changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added documentation to describe my feature.
• I have squashed my commits into logic units.
• I have described the changes in the commit messages.

Other information

If loading fails, CheckMessage will be shown:

?: (weblate.E028) Module 'weblate.addons.consistency' does not define a 'LangauegConsistencyAddon' class in WEBLATE_ADDONS
	HINT: https://docs.weblate.org/en/latest/admin/config.html

This also fixes a typo LangaugeConsistencyAddon to LangaugeConsistencyAddon with backward compatibility.

[nijel]

Merged, thanks for your contribution!