This change converts the reviewable views (and associated utility views)

to TypeScript/spina.
While I was here I disconvered that one of the tests for DiffReviewable

was intended to be async, but didn't take a done callback and was

therefore skipping the meat of the test. After fixing that, it became

evident that the implementation of the test was broken, so it's been

rewritten.

Ran js-tests.
Smoke tested reviewing diffs and file attachments.