R1:3e05ff2e9983

Improve Conpherence behavior for logged out users.

Summary:
There are two issues here I was trying to fix:

* Viewing `/conpherence` by logged out users on `secure` would generate an overheated query on `ConpherenceThreadQuery` `secure` has a ton of wacky threads with bogus names.
* When a user views a specific thread that they don't have permission to see, we attempt to fetch the thread's transactions before applying policy filtering. If the thread has more than 1000 comments, that query will also…