Added basic support for multilingual
Integrate django-parler in the sharedcontent plugin.

This makes sure shared content (e.g. a footer) can be translated too.
The "title" is a translated field, so it can be used in templates if
desired.
Sharedcontent: avoid overwriting the slug in new translations

Also make the slug field less prominent,
as it's a developer feature mainly.
Fix stale ContentItem objects when deleting a translation.

Remove the objects manually in the delete_model_translation() hook.
Merge branch 'multilingual_support' into dev
Update translations
Briefly mention multilingual support in the changelog