Suport netCDFServer name

[jrleeman]

When using NCEI data, they use the older name for NCSS. This makes workshop materials more complicated and requires too much knowledge of the data source for users. We thought this was in 0.7 😭

[lesserwhirls]

There are a couple of ways to go about this. Probably the best way, from an end users point of view, would would involve making sure that this just works©™®:

ncss = dataset.subset()

To do so, we could add a check in the KeyError except:

siphon/siphon/catalog.py

Lines 592 to 596 in 935d195

	try:
	return provider(self.access_urls[service])
	except KeyError:
	raise ValueError(service + ' is not available for this dataset')

and check to see if

1. service is NetcdfSubset and
2. if self.access_urls contains NetcdfServer

If both are true, then we use use NetcdfServer as the service. Otherwise, raise the ValueError as we currently do.

[dopplershift]

See #216 for what seemed to be least horrible to me.