Add publishable flag to antiquarians and works

[tcouch]

For static site conversion antiquarian and work pages should have a publishable flag to determine whether that page should be included when generating static pages. Only Valentina should have permission to do this.

[tcouch]

Ideally we'd like to be able to un-publish

[tcouch]

Also include Fragments, Testimonia, Citing Authors, Citing works.... as publishable / not publishable