This change breaks out the review body (the bit with all the types of comments)

into its own template. The reasoning here is that we're going to want to be

able to re-use this within the change description and initial status update

boxes to show reviews created via status updates.
While I was doing this, I fixed and cleaned up a few things:

The comment_issue tag now handles checking whether an issue is opened, and

  includes the .issue-indicator element. This reduces the amount of

  duplication a bit.
General comments are now displayed first, instead of between file attachment

  comments and diff comments. This is both because they're more likely to be

  truly general, and also a bit better visually because they don't have any

  kind of visual separation other than the issue/reply boxes (there's no

  excerpt the way there is for other comments).
The template for general comments had a few issues with the treatment of rich

  text.
The body-top and body-bottom comments are now included in the same <dl>

  element as all the other comments. This reduces the amount of special casing

  in the CSS.
We had inconsistent borders with the various excerpts. Diff comments had a

  top and bottom border around the commented lines. File attachments had a

  bottom border but no top border. Screenshots had a border on all four sides,

  which was probably the worst of all.
The review dialog has been changed to share the same .review-comments class

  as reviews, rather than duplicating a lot of the CSS rules. This is

  theoretically temporary since we're planning on the big revamp, but that

  revamp should bring them even closer together.
While I was looking at the review dialog, I noticed that there was an extra

  "Markdown Reference" link which is now very silly, since this dialog uses

  individual editors rather than a bunch of text fields.

Created a review with a bunch of different types of comments. Saw that

  everything displayed as correctly.
Verified that the review dialog looked correct as well.