Improve GraphQL documentation and cleanup API

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

js/src/views/Discussions/Create.vue

@@ -70,7 +70,6 @@ export default class CreateDiscussion extends Vue {
           title: this.discussion.title,
           text: this.discussion.text,
           actorId: parseInt(this.group.id, 10),
-          creatorId: parseInt(this.currentActor.id, 10),
         },
       });