Add Issue PDF download link to Newspaper object records

Currently, the Newspaper solution pack does not offer users a way to download a PDF of the complete newspaper issue - only individual pages.

Should offer the option to expose a download link for the PDF datastream, alongside the option to create said datastream. (See attached screenshot)

At its simplest, the generated link would simply point to /islandora/object/[OBJECT:PID]/datastream/PDF/download, with the text "PDF".

Would display in the same way as it does on Citation, Thesius, and PDF objects.