Load new feature image from set of curated options when homepage is loaded/refreshed

[wrenaria]

This feature is part of Phase 3 of the DAMS v1.5 update (#33). Part of v2.

Currently the feature image for Dams is singular and static. We would like to have the feature image be randomly selected on page load and change when page is refreshed by a user.

We need a way to manage these custom images for this feature.

Parameters:

• Each image will be custom cropped for the site, so we cannot just pull directly from existing items.
• There will likely be a second custom cropped image that pairs with the main one for the bottom of the site (see issue Add prominent Browse Collections button above footer on the homepage #36)
• Item title and collection will be displayed and linked to their respective sources (item to item page, collection to collection info page). I would prefer these options were customizable so we can display slightly cleaned up or truncated titles if needed.