records: add link to landing page for local resource files

[GraemeWatt]

The "Additional Publication Resources" widget displays links to DOIs for local resource files attached to a whole submission that directs to the corresponding landing page. However, for non-finalised and Sandbox records, or local resource files attached to individual tables, there is no way to navigate to the landing page other than copying the "Download" URL and manually replacing view=true with landing_page=true. A "Landing page" link should therefore be added above the "Download" button. This issue can be addressed together with #740 on the display-data-license branch. The landing page for local resource files attached to Sandbox records needs a fix made in 601846d.