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/ConfigSchema/schema/HTML.FlashAllowFullScreen.txt

@@ -0,0 +1,11 @@
+HTML.FlashAllowFullScreen
+TYPE: bool
+VERSION: 4.2.0
+DEFAULT: false
+--DESCRIPTION--
+<p>
+    Whether or not to permit embedded Flash content from
+    %HTML.SafeObject to expand to the full screen.  Corresponds to
+    the <code>allowFullScreen</code> parameter.
+</p>
+--# vim: et sw=4 sts=4