I've added getNodeNames and expandNodeNames. For both of these, when we want sorted results (which is always the case for getNodeNames based on current nimble), we need to handle as follows. Since the notion of ordering is not part of nodeRanges, we need to first convert to node chars, one per node, then get the associated calcRange for each to use to sort those node chars. Then if scalar components are requested, convert to varRanges in order to then get the components.

There may be corner cases that make backwards compatibility hard, but not fully sure yet. Also, I still need to consider issue #20 to work through the extent to which nimbleModel may give results in a different order than nimble, in particular in the case of ties and how much we can alleviate that.

I still need to add formal tests (a sketch of some test cases is in test-backwards.R).