Loads this stream by calling River View for data.

def load(self):
    """
    Loads this stream by calling River View for data.
    """
    print "Loading data for %s..." % self.getName()
    self._dataHandle = self._stream.data(
      since=self._since, until=self._until, 
      limit=self._limit, aggregate=self._aggregate
    )
    self._data = self._dataHandle.data()
    self._headers = self._dataHandle.headers()
    print "Loaded %i rows." % len(self)