[add] HTML Purifier added to clean code

inc/3rdparty/htmlpurifier/HTMLPurifier/ConfigSchema/schema/Attr.DefaultInvalidImageAlt.txt

@@ -0,0 +1,8 @@
+Attr.DefaultInvalidImageAlt
+TYPE: string
+DEFAULT: 'Invalid image'
+--DESCRIPTION--
+This is the content of the alt tag of an invalid image if the user had not
+previously specified an alt attribute.  It has no effect when the image is
+valid but there was no alt attribute present.
+--# vim: et sw=4 sts=4