Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/ConfigSchema/schema/HTML.SafeIframe.txt

@@ -0,0 +1,13 @@
+HTML.SafeIframe
+TYPE: bool
+VERSION: 4.4.0
+DEFAULT: false
+--DESCRIPTION--
+<p>
+    Whether or not to permit iframe tags in untrusted documents.  This
+    directive must be accompanied by a whitelist of permitted iframes,
+    such as %URI.SafeIframeRegexp, otherwise it will fatally error.
+    This directive has no effect on strict doctypes, as iframes are not
+    valid.
+</p>
+--# vim: et sw=4 sts=4