prototype distinguishes:
- content shares (link, download, view) versus status attachments (download)
- files (with title, description) versus images (fullwidth)
- has preview versus no preview versus preview in progress
Please study prototype/./_includes/post.html when making changes here.
NB the prototype assumes that multiple attachments are either all images
or else are all files. Implementation will need to split that into
a multi-file + multi-image renderer.