Fixed: usage of owner side / inversed side on SocialAction / Evaluation

In a ManyToMany relationship, doctrine does take care only of the owning
side of a relationship to inspect changes.

([see
documentation](https://www.doctrine-project.org/projects/doctrine-orm/en/current/reference/unitofwork-associations.html#important-concepts))

This commit mark as "internal" the methods add/removeSocialAction on the
inversed side (`Evaluation`) and let the methods add/removeEvaluation
on the owning side (`SocialAction`) update the inversed side.

The usage is also adapted into SocialWorkMetadata's importer.

src/Bundle/ChillPersonBundle/Service/Import/SocialWorkMetadata.php

@@ -193,7 +193,7 @@ final class SocialWorkMetadata implements SocialWorkMetadataInterface
         /** @var Evaluation $eval */
         $eval = $this->getOrCreateEntity($this->evaluationRepository, 'title', ['fr' => $evaluationTitle]);
         $eval->setTitle(['fr' => $evaluationTitle]);
-        $eval->addSocialAction($socialAction);
+        $socialAction->addEvaluation($eval);
 
         $this->entityManager->persist($eval);