Revert "remove htmlpurifier"

This reverts commit c21a462d52.

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

@@ -0,0 +1,14 @@
+Attr.IDPrefixLocal
+TYPE: string
+VERSION: 1.2.0
+DEFAULT: ''
+--DESCRIPTION--
+Temporary prefix for IDs used in conjunction with %Attr.IDPrefix.  If you
+need to allow multiple sets of user content on web page, you may need to
+have a seperate prefix that changes with each iteration.  This way,
+seperately submitted user content displayed on the same page doesn't
+clobber each other. Ideal values are unique identifiers for the content it
+represents (i.e. the id of the row in the database). Be sure to add a
+seperator (like an underscore) at the end.  Warning: this directive will
+not work unless %Attr.IDPrefix is set to a non-empty value!
+--# vim: et sw=4 sts=4