Use symbolic link for foreign key inside application

Signed-off-by: Michal Čihař <michal@cihar.com>
Use specific imports for models

Signed-off-by: Michal Čihař <michal@cihar.com>
Document overrides

Signed-off-by: Michal Čihař <michal@cihar.com>
Avoid explicit import

Signed-off-by: Michal Čihař <michal@cihar.com>