No public access to actually used measurement windows

[terrorfisch]

As #780 shows there is the requirement to get the measurement windows that correspond to the measured data in a convinient and stable way.

I think the best way is to add a get_measure_times(self, program_name) -> Tuple[np.array, np.array] to the DAC interface.

However, this is not a general solution because the DAC might perform some analysis that obscures how the measurement times are related with the actual output.