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/graphql/member.ts

@@ -100,3 +100,12 @@ export const REMOVE_MEMBER = gql`
     }
   }
 `;
+
+export const JOIN_GROUP = gql`
+  mutation JoinGroup($groupId: ID!) {
+    joinGroup(groupId: $groupId) {
+      ...MemberFragment
+    }
+  }
+  ${MEMBER_FRAGMENT}
+`;