Style "Files" section as a card to keep consistent with rest of sidebar on item show page

[murny]

From #1666

For objects with multiple files, the files section looks quite a bit different then everything else in this sidebar. It be nice to keep this consistent with community/collections and usage cards and put the files section into a card component (https://getbootstrap.com/docs/4.5/components/card/). Card header would be "Files" and body contains all file objects with a download all button. Think this would greatly improve the look of the sidebar and keep it consistent with the facets sidebar on search index.

Example here:

Notice how Files section looks quite different and out of place to Community/Collection and Usage cards. We should keep everything consistent where possible.

A quick mockup might looked like the following: