Add vim modelines to all files.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

library/HTMLPurifier/ConfigSchema/schema/HTML.SafeEmbed.txt

@@ -10,4 +10,5 @@ DEFAULT: false
     element and will cause your website to stop validating. You probably want
     to enable this with %HTML.SafeObject.
     <strong>Highly experimental.</strong>
-</p>
+</p>
+--# vim: et sw=4 sts=4