Allow to join an open group

Also:

* Refactor interacting with a remote event so that you can interact with
  a remote group as well
* Add a setting for group admins to pick between an open and invite-only
  group
* Fix new groups without posts/todos/resources/events/conversations URL
  set
* Repair local groups that haven't got their
  posts/todos/resources/events/conversations URL set
* Add a scheduled job to refresh remote groups every hour
* Add a user setting to pick when to receive notifications when there's
  new members to approve (will be used when this feature is available)
* Fix pagination for members

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

js/src/views/Discussions/Create.vue

@@ -63,13 +63,14 @@ export default class CreateDiscussion extends Vue {
 
   async createDiscussion(): Promise<void> {
     try {
+      if (!this.group.id || !this.currentActor.id) return;
       const { data } = await this.$apollo.mutate({
         mutation: CREATE_DISCUSSION,
         variables: {
           title: this.discussion.title,
           text: this.discussion.text,
-          actorId: this.group.id,
-          creatorId: this.currentActor.id,
+          actorId: parseInt(this.group.id, 10),
+          creatorId: parseInt(this.currentActor.id, 10),
         },
       });