update excluded channel treatment

[clark2668]

This creates a dataset object that contains the excluded channels (according to the yaml file), plus the hpols or the vpols. This way if you want to compute a vpol only variable, you can do like:

snr_vpol = snr.get_snr(wavebundle, excluded_channels = d.excluded_channels_and_hpol)

[marcomuzio]

Looks good to me!

[clark2668]

Thank you!