Added french translation files for backend and frontend.

frontend/fr/catalogue.json

@@ -0,0 +1,10 @@
+{
+    "catalogue": {
+        "volume": "Volume",
+        "public": "Public",
+        "not_public": "Not public",
+        "title_main": "Museum-Digital",
+        "title_sub": "Catalogue of objects for",
+        "generated": "Generated"
+    }
+}