Link image and title in slideshow modal out to document

[marlo-longley]

Fixes DLME #1373

It was suggested to solve this issue by making a change in the upstream repo here

Changes made:

• Removes suppress_link: true option from the image in the slideshow modal
• Adds link to item heading in slideshow modal to document
• Modifies CSS to cover new <a> tags
• Modifies test to ignore search session tracking and handle linking

[marlo-longley]

@cbeer I addressed your comments - thanks for your help on this!