Observable client-side preferences and configs

[lbwexler]

Its always been a little strange that preferences and configs are only updated on the client when the entire page is refreshed. We think it would be very natural to push or poll for updates, and make the collections observable on the client.

Just doing so will not automatically make all hoist and app code reactive to these, but it is the first step, and we think its a capability that could be gradually exercised if we made it available.