Copies the spikes and optionally converts the spike times.
            (when the keyword units is not None)

def copy(self,**kwargs):
        """
            Copies the spikes and optionally converts the spike times.
            (when the keyword units is not None)
        """
        new_spike_times = LabeledMatrix(self.spike_times.matrix,self.spike_times.labels) # copies the data
        return SpikeContainer(new_spike_times, copy_from=self,**kwargs)