[BUGFIX] Properly detect "many" relation

Method \TYPO3\CMS\Vidi\Tca\ColumnService::hasRelationMany() relies
on "maxitems" or "foreign_table_field" properties to decide
whether a field has a "many" relation or not. This is not
sufficient. A one-to-many relation may use a MM table if it needs
to be bidirectional. In such a case "maxitems" will be 1, but
the relation still needs to be detected as a "many" relation.