Add button is not displayed in the relation content

In #63, the add button has been moved to the table header. Now it's not displayed anymore on the relation content. Only if the following statement https://github.com/araise-dev/TableBundle/pull/63/files#diff-8bdde9f0b8b297297dd6f7163d5c665e910c62d6f17237f1be83c5004fd103efL1-L2 is true. But sometimes you wouldn't define a table title or enable extensions.