Replace existing autoloader with Composer-supplied

- Move Friendica namespace to `src`
- Move required `ezyang/htmlpurifier` to vendor
- Remove existing static autoloader
- Change boot.php reference to the autoloader

vendor/ezyang/htmlpurifier/library/HTMLPurifier/URIScheme/file.php

@@ -0,0 +1,44 @@
+<?php
+
+/**
+ * Validates file as defined by RFC 1630 and RFC 1738.
+ */
+class HTMLPurifier_URIScheme_file extends HTMLPurifier_URIScheme
+{
+    /**
+     * Generally file:// URLs are not accessible from most
+     * machines, so placing them as an img src is incorrect.
+     * @type bool
+     */
+    public $browsable = false;
+
+    /**
+     * Basically the *only* URI scheme for which this is true, since
+     * accessing files on the local machine is very common.  In fact,
+     * browsers on some operating systems don't understand the
+     * authority, though I hear it is used on Windows to refer to
+     * network shares.
+     * @type bool
+     */
+    public $may_omit_host = true;
+
+    /**
+     * @param HTMLPurifier_URI $uri
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool
+     */
+    public function doValidate(&$uri, $config, $context)
+    {
+        // Authentication method is not supported
+        $uri->userinfo = null;
+        // file:// makes no provisions for accessing the resource
+        $uri->port = null;
+        // While it seems to work on Firefox, the querystring has
+        // no possible effect and is thus stripped.
+        $uri->query = null;
+        return true;
+    }
+}
+
+// vim: et sw=4 sts=4