Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/ConfigSchema/schema/Attr.EnableID.txt

@@ -0,0 +1,16 @@
+Attr.EnableID
+TYPE: bool
+DEFAULT: false
+VERSION: 1.2.0
+--DESCRIPTION--
+Allows the ID attribute in HTML.  This is disabled by default due to the
+fact that without proper configuration user input can easily break the
+validation of a webpage by specifying an ID that is already on the
+surrounding HTML.  If you don't mind throwing caution to the wind, enable
+this directive, but I strongly recommend you also consider blacklisting IDs
+you use (%Attr.IDBlacklist) or prefixing all user supplied IDs
+(%Attr.IDPrefix).  When set to true HTML Purifier reverts to the behavior of
+pre-1.2.0 versions.
+--ALIASES--
+HTML.EnableAttrID
+--# vim: et sw=4 sts=4