Support of PubMed Central links in Full Text Sources

[ehenneken]

This issue is for allowing the addition of a new item to the Full Text Sources box. This is for the support of PubMed Central links (both HTML and PDF). When records have such links, the Solr field esources will have one or both of the values PMC_HTML or PMC_PDF. The label for these links should be PMC and it should go at the very bottom of the ordering list in src/components/AbstractSources/model.ts:

export const DEFAULT_ORDERING = [
  Esources.ADS_PDF,
  Esources.ADS_SCAN,
  Esources.INSTITUTION,
  Esources.PUB_PDF,
  Esources.PUB_HTML,
  Esources.EPRINT_PDF,
  Esources.EPRINT_HTML,
  Esources.AUTHOR_PDF,
  Esources.AUTHOR_HTML,
  Esources.PMC_PDF,
 Esources.PMC_HTML,
];

It looks like this file needs to be updated as well: src/api/search/types.ts.