Create a clear file download UI, with different presentation for single- vs...
Create a clear file download UI, with different presentation for single- vs multi-file items. Closes DUK-28.
- use a primary call-to-action button for single-file, secondary buttons for multi-
- render fontawesome icons in the download buttons keyed off of the file extension
- don't show a thumbnail image on the item page if we don't have one