This introduces unit tests for RB.PageView. As this class becomes more

crucial to the rendering of pages, we need to ensure its behavior

continues to work as expected. The new unit tests ensure that by

covering all the current aspects of the page, including state

calculation, rendering, event handling, and drawer setup. These are

tested in all the various modes (mobile/desktop, full-page content,

and sidebar modes).
Given that RB.PageView (and RB.HeaderView, one of the utility views

it uses) modify the actual page structure itself (which interferes with

the page running the tests), they needed to be updated to allow callers

to pass in specific page elements to use. These will have no effect on a

typical page render, but allow unit tests to sandbox the page

modifications that the views want to make.
The views have also been updated to clean up any global event registration

they perform.
This also fixes up the JavaScript unit test page to properly load the

stylesheet for the page, which regressed during cleanup of the base

template in commit 123665fa1695670cd7ec3d5fe9ab26cb8057bce1.

All unit tests pass.