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.