This introduces new machinery for automatically updating parts of the

review request page in response to updates from the server. It

specifically targets the new status updates feature, but is built to

eventually allow most or all of the page to periodically update as

needed.
Entries can now tell the page that they want to watch for updates, and

supply a polling frequency. The lowest frequency wins, and at each poll

interval, the server will provide metadata and HTML for each requested

entry being polled. If the data is newer than what the page has, it will

update the model attributes and view's HTML appropriately. This can

continue indefinitely or be turned off when needed.
The entries supporting status updates will watch for updates if any

status update is in the pending state, and will stop polling once that's

no longer the case.
Going forward, we'll be able to start moving to this and away from the

last-updated checks, handling dynamic updating of conversations and of

the review request itself in response to changes made in other tabs.

This is a larger project and does not target 3.0, but the foundation is

there for the future.

Unit tests pass.
Created status updates in pending mode. Saw that the page periodically

checked for updates. Switched the status update to a different mode and

saw that, after only a short wait, that the entry updated to reflect the

new mode.
Checked that the issue summary table updated appropriately based on issues

filed on the status update.