Show child categories in export

Currently exports only display the parent category in the category column. Sometimes it's important for our client to be able to filter by subcategories, especially when exporting the results. We recommend with @Armand_OSP that we keep the two existing catégories : - category/id - category/name/fr In the cell we'll just use a json format : cat_parent : { "cat_child":{cat_grandchild"}} That way a developper can still parse it.