Revert "remove htmlpurifier"

This reverts commit c21a462d52.

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

@@ -0,0 +1,8 @@
+HTML.TargetBlank
+TYPE: bool
+VERSION: 4.4.0
+DEFAULT: FALSE
+--DESCRIPTION--
+If enabled, <code>target=blank</code> attributes are added to all outgoing links.
+(This includes links from an HTTPS version of a page to an HTTP version.)
+--# vim: et sw=4 sts=4