Revert "remove htmlpurifier"

This reverts commit c21a462d52.

lib/htmlpurifier/library/HTMLPurifier/ConfigSchema/schema/Output.TidyFormat.txt

@@ -0,0 +1,25 @@
+Output.TidyFormat
+TYPE: bool
+VERSION: 1.1.1
+DEFAULT: false
+--DESCRIPTION--
+<p>
+    Determines whether or not to run Tidy on the final output for pretty
+    formatting reasons, such as indentation and wrap.
+</p>
+<p>
+    This can greatly improve readability for editors who are hand-editing
+    the HTML, but is by no means necessary as HTML Purifier has already
+    fixed all major errors the HTML may have had. Tidy is a non-default
+    extension, and this directive will silently fail if Tidy is not
+    available.
+</p>
+<p>
+    If you are looking to make the overall look of your page's source
+    better, I recommend running Tidy on the entire page rather than just
+    user-content (after all, the indentation relative to the containing
+    blocks will be incorrect).
+</p>
+--ALIASES--
+Core.TidyFormat
+--# vim: et sw=4 sts=4