[JRO] Pull partial into view

* The looping and rendering a partial takes more time than it is worth so pulling it in might help speed things up incrementally.
* Loading the topics/private topics before rendering the page will keep
  the lazy loading from firing off in the middle of rendering the page.
* Preload user relations
* NullUser needs these fake associations
[JRO] Move activity update to the background queue

Shaves about 4 sql queries off Topics#index. Not bad.
[JRO] Reduce some queries