code: public static void cancelTasksByGroup(Context context, int groupId, int reason,
        CancelListener cancelListener) {
      cancelTasks(context, GroundyService.class, groupId, reason, cancelListener);
    }
docs: Cancels all tasks of the specified group w/ the specified reason.
  
  @param context used to interact with the service
  @param groupId the group id to cancel
  @param cancelListener callback for cancel result