There are several improvements that can be made to the way that we display and

manage file attachments. Currently, when looking at a review request draft we

have no way of knowing whether a file attachment is a draft or not. It would

be nice to be able to distinguish the draft file attachments from the published

ones. It would also be nice to be able to see if a draft is a new revision of

an attachment, a completely new one, or an update to an existing one (e.g. one

with an updated caption). We also can't tell when a file attachment is

pending deletion on a review request draft, i.e. when its been deleted from

the draft but the draft has not been published yet.
This change aims to address all of those issues. Now, we use a label to display

the state of file attachments on a review request draft (except for published

attachments). It's easier to undo draft updates to the attachments with a

new "Delete Draft" action, which can delete draft revisions and redisplay

the previously published attachment, delete new drafts, or undo any changes

to the caption. And, instead of making attachments disappear after deleting

them from a review request draft, we display them as pending deletion and

allow users to undo the deletion with an "Undo Delete" action.

Ran unit tests.
Ran JS unit tests.
Lots of manual testing, uploading/updating/deleting file attachments,

  changing the state, changing the caption, updating, reviewing, commenting,

  testing the new actions.
Made sure user file attachments and file attachments thumbnails in change

  descriptions were not affected.
Tested trying to view a draft review request as a user who doesn't have

  permission for the draft, saw that no file attachment states or any of

  the new actions appeared.