Small improvements to the review CSS.
Small improvements to the review CSS.

This change makes a few small improvements to the look of the review detail
generally (and review boxes in particular). I'm planning on doing a somewhat
more invasive clean-up like I did to the review request box, but that will come
later.

The changes herein are:

- Removal of the 0.5em margin around the review/changedesc boxes, which was so
  small as to be unnoticable (except when I added another full-width box that
  didn't match the width of the review request box).
- Cleanup of the bottom margin of the page to avoid extra space.
- Tweaking of margins and padding to make it so the expand/collapse buttons had
  the same amount of spacing on both review and changedesc boxes.
- Tweaking of spacing for collapsed boxes so that there wasn't any extra height
  that didn't need to be there.

Testing done:
Looked at the page in both desktop and mobile mode. Checked that everything
changed looked correct.

Reviewed at https://reviews.reviewboard.org/r/8341/

chipx86/reviewboard,davidt/reviewboard,davidt/reviewboard,davidt/reviewboard,davidt/reviewboard,brennie/reviewboard,reviewboard/reviewboard,brennie/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,brennie/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard,brennie/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,sgallagher/reviewboard