Added french translation files for backend and frontend.

frontend/fr/assotag.json

@@ -0,0 +1,7 @@
+{
+    "assotag": {
+        "objects_to_keywords": "Objects for keywords",
+        "more_objects_to_keywords": "More objects in relation to this keyword",
+        "more_about_keyword": "More about this keyword and more objects at museum-digital (all versions)"
+    }
+}