code: public static void cancelTasksByGroup(Context context, int groupId,
        CancelListener cancelListener) {
      cancelTasksByGroup(context, groupId, GroundyTask.CANCEL_BY_GROUP, cancelListener);
    }
docs: Cancels all tasks of the specified group. The tasks get cancelled with the {@link
  GroundyTask#CANCEL_BY_GROUP} reason.
  
  @param context used to interact with the service
  @param groupId the group id to cancel
  @param cancelListener callback for cancel result