Indicate unread submissions in source view

[garrettr]

In the "Sources" view of the Document Interface, we indicate the number of unread submissions for each source, and provide a handy button to download just the unread submissions as an archive.

However, in the individual "Source" view, we do not indicate which submissions are unread.

This makes it difficult to figure out which submissions are unread in the Source view, particularly for sources with many submissions. It should be easy to fix this by adding an icon to the row for each submission in the Source view.

We might also consider adding a "Select all unread" button to the Source view, or another "Download unread" button on the source view (to save journalists from having to hit the Back button and potentially scroll through a long list of sources when they realize they want to download all unread after already having gone to a Source page).