This is the first part in improving the diff comment bubbles.

The tooltip previews for the comment text will show the full rendered comment text together with the name of the reviewer, with the size of the tooltip maximized to the screen width.

Updated js tests as the comment reviewer needs to be loaded with each comment.

Ran tests, added markdown and plain text comments to check visually.
Added unit testing for XSS vulnerabilites. Manually checked by creating comments containing script tags for both markdown and plain text, scripts were escaped and not executed for both first load of the page and subsequent asynchronous updating of comments.