new NCBI Nucleotide web translator

Using the Entrez Eutils JSON API. This is a translator for datasets, and therefore has some limitations, e.g. apparently no author information.
Actually, I'd say ditch the `[-.]` part and just account for `\.`. The only reason that we have that in PubMed is because there are some annoying proxies that do some unusual URL transformations. They're generally rare (or maybe pubmed is a special case), but given the volume of PubMed users we've had reports of the translator not working, so we hacked around it. I'm not too concerned about this case here.