@classmethod
  def QueryActivities(cls, client, viewpoint_id, callback, excl_start_key=None, limit=None):
    def _OnQueryActivities(activities):
      callback((activities, activities[-1].activity_id if len(activities) > 0 else None))

    Activity.RangeQuery(client, viewpoint_id, range_desc=None, limit=limit, col_names=None,
                        callback=_OnQueryActivities, excl_start_key=excl_start_key)
Queries activities belonging to the viewpoint (up to 'limit' total) for
dataset/ETHPy150Open viewfinderco/viewfinder/backend/db/viewpoint.py/Viewpoint.QueryActivities