Added GroupPinnedStatuses

• Added:
- GroupPinnedStatuses
- controllers for timeline, creation, deletion
- redux actions, reducers for creation, deletion
- timeline fetching in timelines action
- options to pin, unpin in status options popover for group admin

app/models/concerns/group_interactions.rb

@@ -17,6 +17,10 @@ module GroupInteractions
       follow_mapping(GroupAccount.where(group_id: target_group_ids, account_id: account_id, role: :moderator), :group_id)
     end
 
+    def pinned?(status)
+      group_pinned_statuses.where(group_id: status.group_id, status: status).exists?
+    end
+
     private
 
     def follow_mapping(query, field)