Homestyx hydra

R1:a13db0a3ec0c

Allow Controllers to return a wider range of "response-like" objects

Summary:
Ref T1806. Ref T5752. Currently, `handleRequest()` needs to return an `AphrontResponse`, but sometimes it's really convenient to return some other object, like a Dialog, and let that convert into a response elsewhere.

Formalize this and clean up some of the existing hacks for it so there's less custom/magical code in Phabricator-specific classes and more general code in Aphront classes.

More broadly, I want to clean up T5752…
Repository: R1 hydra
Commit Date: Sep 1 2015