Allow users to set a line-height in their monospaced font preference

Summary: Ref T10959. This does not fix the problem because the `.differential-diff td` rule is still stronger, but it does let you choose a more compact or breezy style for remarkup blocks and pastes.

Test Plan:
  - Set font to `24px / 48px impact`.
  - Viewed a paste, saw lovely readable text.
  - Viewed an inline code block which was very easy on the eyes.

{F1310420}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10959

Differential Revision: https://secure.phabricator.com/D15904

src/applications/settings/storage/PhabricatorUserPreferences.php

@@ -113,7 +113,7 @@ final class PhabricatorUserPreferences extends PhabricatorUserDAO {
 
   public static function filterMonospacedCSSRule($monospaced) {
     // Prevent the user from doing dangerous things.
-    return preg_replace('/[^a-z0-9 ,".]+/i', '', $monospaced);
+    return preg_replace('([^a-z0-9 ,"./]+)i', '', $monospaced);
   }
 
 }