Images of Discover do not have altText (ADA)

[CharlesChapman]

In the data definition for the "Results" for Discover, we don't prompt for "alternate Text" to accompany the image for ADA compliance. This needs to be remedied in the Data Definition, then we also need to modify the format in Cascade that's outputting that image so the final webpage markup uses that value for the altText on the IMG tags.

Same issue for the masthead images (fallback images) in the landing pages for each section within Discover.