Modify Celerity to emit required resources on Ajax responses
Summary: Companion diff to D4003.
Test Plan: Rigged up a response which loaded a CSS file with body { background: red; }, verified page turned red after I clicked the button.
Reviewers: vrana, chad, btrahan
Reviewed By: chad
CC: aran
Maniphest Tasks: T2086
Differential Revision: https://secure.phabricator.com/D4004