The newer version of jQuery we're using on release-4.0.x has a behavior

difference in .show() where it won't override a default style of

display: none. This meant that the way we were showing/hiding the

various pages of the upload diff UI (used both for the "Update Diff" and

"New Review Request" flows) wasn't working.
This change makes it so we don't have any default visibility and instead

handle all the showing/hiding via JavaScript.

Loaded the New Review Request and Update Diff UIs and saw the correct

view.