The review request, diff viewer, and review UI pages all need a large

payload for the options for the page views (RB.ReviewablePageView, in

particular). We generated this with an includable template, but over

time this has grown to the point where it's a pain to maintain and not

particularly efficient.
This change replaces the template with a template tag. The new tag

generates the same data, but does so server-side, encoding to JSON at

the end (instead of having to encode various bits of data through other

template tags). This should speed up render times and make it much

easier for us to augment the data down the road.
This is part of a larger set of changes that are needed for dynamic

updating of the review request page.

Tested that all the pages worked correctly. All data was provided and

the UIs still work as normal.
Performed JSON comparisons of the old and new data. Aside from some

fields that are no longer provided if empty, the data has not changed.