Add RefSeq type provider

[n7581769]

At present, the type provider only supports GenBank, though there are routes to use RefSeq data that lead to "unsupported" message outputs. Once we are happy with the state of the GenBank type provider, we may look into creating a RefSeq type provider too.

[n7581769]

Though we are probably not finished with the GenBank type provider yet, an implementation of a RefSeq type provider has been added in f613edc. It works in the same way in that a species and accession can be specified, either as a full name or a pattern. The only difference to the package user is that the type provider is invoked with "RefSeqTypeProvider" rather than "GenBankTypeProvider". The metadata that is returned may be different but is still accessible with the existing types in the project.