This change adds the unified banner, a major new UI feature in Review

Board 6.
This new banner replaces several existing banners:

The review request draft banner
The pending review banner
Review reply banners (at least the ones that float)

The goal here is twofold. First, we want to make it very clear whenever

there's any unpublished work (often review reply drafts can get lost in

long pages). Second, we want to enable people to publish everything all

in one go (the typical use case being publishing a bunch of review

replies and a review request update all together).
This also gives us room for future work:

We have space at the right hand side of the banner for a future

  block showing info about the current review, popping up into a

  redesigned review dialog.
We have a "dock" area (currently empty, but present in the DOM and

  properly styled), which we intend to use for a quick file switcher in

  the diffviewer, and possibly other things.

This is mostly complete. The current things left on my to-do list are:

Further testing of the banner in mobile mode. Right now interaction

  with the menus has some problems but it's possible that's just

  Firefox's devtools.
Possibly moving the "Add General Comment" action into the review menu.
Add more js-tests.

Ran js-tests.
Ran python unit tests.
Tested all different combinations of review requset changes, reviews,

  and review replies. Saw that the draft mode selector showed the

  correct options.
Tested publishing with individual items and as a batch.
Tested discard with various individual items.
Tested the change description field.
Tested the new actions (create review, edit review, ship it) that live

  in the "Review" menu.