Use lazy() for PlaceholderRelation, so ContentType is read at a sane time.
Use lazy() for PlaceholderRelation, so ContentType is read at a sane time.

This avoids import errors, and syndb errors because the ContentType was
read at model setup/construction instead of runtime execution.

edoburu/django-fluent-contents,ixc/django-fluent-contents,django-fluent/django-fluent-contents,jpotterm/django-fluent-contents,jpotterm/django-fluent-contents,ixc/django-fluent-contents,pombredanne/django-fluent-contents,ixc/django-fluent-contents,edoburu/django-fluent-contents,django-fluent/django-fluent-contents,edoburu/django-fluent-contents,pombredanne/django-fluent-contents,pombredanne/django-fluent-contents,django-fluent/django-fluent-contents,jpotterm/django-fluent-contents