Add a Research Help link field for a collection and display it

[seanaery]

Some collections will have a page or indeed several pages of HTML, images, etc. that aim to assist a researcher with context or discovery within a collection. This content exceeds the limitations of abstract & description field metadata on collection objects, and also stretches beyond what's suitable for "About" pages in ddr-portals.

Because this should be supported for any collection--even those not configured in ddr-portals--there is a likely dependency on administrative metadata specified in ddr-models. The link should be able to point to any URL in order to accommodate guides in LibGuides, Drupal, or elsewhere.

Noted in stakeholder feedback (DVS Review 5/26/16). Also relevant to 1990s-era digital collections with Research Guides (e.g., Ad*Access, EAA, Sheet Music).

[seanaery]

Revised typo in the issue title. Research Help (contact point) is already covered--this is about adding a Research Guide.