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/Strategy.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * Supertype for classes that define a strategy for modifying/purifying tokens.
+ *
+ * While HTMLPurifier's core purpose is fixing HTML into something proper,
+ * strategies provide plug points for extra configuration or even extra
+ * features, such as custom tags, custom parsing of text, etc.
+ */
+
+
+abstract class HTMLPurifier_Strategy
+{
+
+    /**
+     * Executes the strategy on the tokens.
+     *
+     * @param HTMLPurifier_Token[] $tokens Array of HTMLPurifier_Token objects to be operated on.
+     * @param HTMLPurifier_Config $config
+     * @param HTMLPurifier_Context $context
+     * @return HTMLPurifier_Token[] Processed array of token objects.
+     */
+    abstract public function execute($tokens, $config, $context);
+}
+
+// vim: et sw=4 sts=4