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/AttrDef/HTML/Length.php

@@ -0,0 +1,56 @@
+<?php
+
+/**
+ * Validates the HTML type length (not to be confused with CSS's length).
+ *
+ * This accepts integer pixels or percentages as lengths for certain
+ * HTML attributes.
+ */
+
+class HTMLPurifier_AttrDef_HTML_Length extends HTMLPurifier_AttrDef_HTML_Pixels
+{
+
+    /**
+     * @param string $string
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return bool|string
+     */
+    public function validate($string, $config, $context)
+    {
+        $string = trim($string);
+        if ($string === '') {
+            return false;
+        }
+
+        $parent_result = parent::validate($string, $config, $context);
+        if ($parent_result !== false) {
+            return $parent_result;
+        }
+
+        $length = strlen($string);
+        $last_char = $string[$length - 1];
+
+        if ($last_char !== '%') {
+            return false;
+        }
+
+        $points = substr($string, 0, $length - 1);
+
+        if (!is_numeric($points)) {
+            return false;
+        }
+
+        $points = (int)$points;
+
+        if ($points < 0) {
+            return '0%';
+        }
+        if ($points > 100) {
+            return '100%';
+        }
+        return ((string)$points) . '%';
+    }
+}
+
+// vim: et sw=4 sts=4