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.
For multiples, i think it's best to migrate the above code to a separate function and call it from detectWeb as well. This ensures that the multiples icon does not show up in the URL bar if there are actually no results to import. [YouTube translator](https://github.com/zotero/translators/blob/c1d9ed981cee88f5a89a1abffae069c5fcdf19c3/YouTube.js#L26) has a pretty simple example of this