Use a spinner icon instead of the word "Loading" for thumbnails that are
being processed in the background in a batch upload.
Also use morphdom to update thumbnails so we only update the parts of
the DOM that actually changed.
Add data attributes to thumbnails on the /uploads, /upload_media_assets,
and /media_assets pages. Add a `data-is-posted` attribute for styling
thumbnails based on whether they've already been posted.
This page shows each individual file you've uploaded. This is different
from the regular uploads page because files in multi-file uploads are
not grouped together.
