This change does a major cleanup for the HTML and CSS related to the review

request box. There are no real functional changes, but lots of small refactors

and cleanups:

All styles relating to the review request box now live in review-request.less
Spacing and alignment has been fixed throughout. Examples of this include a

  1px misalignment that we had between the "Summary:" box and the rest of the

  boxes, a 4px misalignment on the pencil icon for fields that didn't have any

  content, and a big handful of places that just grabbed spacing values out of

  a hat. Things now rely on a common "review-request-section" class which sets

  the spacing around the box.
IDs in this box now consistently use hyphens, where before we had a mix.
Use of rem rather than em (since it's supported on all the browsers we

  now care about).
Menus now actually use our common .has-menu and .menu rules, rather than

  completely reimplementing them.
Better namespacing for all the action classes, swapping out the very general

.action* for .review-request-action*
Useless elements were removed, including the use of {% box %} around the

  review request, since we were overriding all the box styles anyway.
A bunch of totally obsolete style rules (relevant classes/IDs didn't exist

  anymore) were removed.

Tested a variety of browsers on both desktop and mobile for the appearance and

functionality of the review request detail, diff viewer, and review UI pages.