The review request page does some long-running requests to fetch new

updates to various parts, including entries and the issue summary table.

The entries all had an updated timestamp included, and on the client

side we'd check to make sure there actually was an update, but the issue

summary table did not. This change adds a new timestamp to the update

payload for this, and checks that timestamp client-side to prevent us

from doing unnecessary DOM updates.

Ran python tests.
Ran js-tests.
Verified that when just looking at an unchanged page, the issue

  summary table was not being updated in the DOM.
Changed some issue state from another tab and saw the issue summary

  table reload correctly.