Add preview and drafts to audits

Summary: Add comment previews and saved drafts to audits, like Maniphest /
Differential.

Test Plan: Typed stuff into the box. Got a preview. Reloaded page. Stuff was
still there. Submitted comment. Stuff is gone.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran, epriestley

Maniphest Tasks: T904

Differential Revision: https://secure.phabricator.com/D1699

src/applications/audit/controller/addcomment/PhabricatorAuditAddCommentController.php

@@ -40,6 +40,7 @@ final class PhabricatorAuditAddCommentController
       ->setAction($request->getStr('action'))
       ->setContent($request->getStr('content'));
 
+
     id(new PhabricatorAuditCommentEditor($commit))
       ->setUser($user)
       ->addComment($comment);
@@ -48,6 +49,14 @@ final class PhabricatorAuditAddCommentController
     $handles = id(new PhabricatorObjectHandleData($phids))->loadHandles();
     $uri = $handles[$commit_phid]->getURI();
 
+    $draft = id(new PhabricatorDraft())->loadOneWhere(
+      'authorPHID = %s AND draftKey = %s',
+      $user->getPHID(),
+      'diffusion-audit-'.$commit->getID());
+    if ($draft) {
+      $draft->delete();
+    }
+
     return id(new AphrontRedirectResponse())->setURI($uri);
   }