[CORE] Move core plugins to a new modules directory

For reference (raised by rozzin in IRC):

* http://foldoc.org/module
* http://foldoc.org/library
* http://foldoc.org/plugin

As noted by XRevan86, modules are not necessarily non-essential.
As we will keep the modules directory in GS root [therefore, near to
plugins/], it is evidenced the difference between both.

This is a simple yet fundamental structural change. It doesn't change
functionality but makes clearer the way we understand GNU social's
internals.

modules/HTMLPurifierSchemes/lib/htmlpurifier/urischeme/gopher.php

@@ -0,0 +1,36 @@
+<?php
+
+/**
+ * Validates gopher
+ */
+class HTMLPurifier_URIScheme_gopher extends HTMLPurifier_URIScheme
+{
+    /**
+     * @type int
+     */
+    public $default_port = 70;
+
+    /**
+     * @type bool
+     */
+    public $browsable = true;
+
+    /**
+     * @type bool
+     */
+    public $hierarchical = true;
+
+    /**
+     * @param HTMLPurifier_URI $uri
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool
+     */
+    public function doValidate(&$uri, $config, $context)
+    {
+        $uri->userinfo = null;
+        return true;
+    }
+}
+
+// vim: et sw=4 sts=4