Allow users to set whether or not textareas are monospaced.

Summary:
Some users like monospaced textareas and others don't.
This introduces an option to set this as a user preference.

Test Plan: Enabled and saw monospaced textareas, disabled and saw non-monospaced textareas.

Reviewers: epriestley

CC: aran, Korvin

Maniphest Tasks: T2114

Differential Revision: https://secure.phabricator.com/D4037

src/applications/diffusion/controller/DiffusionCommitController.php

@@ -575,7 +575,8 @@ final class DiffusionCommitController extends DiffusionController {
           ->setLabel('Comments')
           ->setName('content')
           ->setValue($draft)
-          ->setID('audit-content'))
+          ->setID('audit-content')
+          ->setUser($user))
       ->appendChild(
         id(new AphrontFormSubmitControl())
           ->setValue($is_serious ? 'Submit' : 'Cook the Books'));