Allow individual work to be marked as scholarly, to enable Google Scholar meta tags and sitemap indexing

[kerchner]

Currently we only add Google Scholar compliant <meta> tags, and sitemap.xml entries, for ETDs. Once we observe that Google Scholar indexes those works, we can move on to allow other works to be individually identified as scholarly. This might take the form of a metadata field implemented as a checkbox. The <meta> tags for citation_type and dc:type would need to derive the type from the resource_type value.

Ref: https://scholar.google.com/intl/en/scholar/inclusion.html#indexing