Add legacy attributes on ReviewablePageView for extensions.

Review Request #9438 — Created Dec. 14, 2017 and submitted — Latest diff uploaded

Information

Review Board
release-3.0.x
c16a300...

Reviewers

The view/model cleanup for the reviewable pages removed some attributes
needed by extensions. The reviewRequest attribute was previously
fixed, but the pendingReview attribute remained broken. This adds this
attribute back, and listens for any changes on the model in order to
update the view (which currently does not happen, but this might change
for pending reviews as things become more dynamic).

Tested that Power Pack and rbstopwatch both worked. Previously, rbstopwatch
was broken.

Unit tests pass.