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.BlockWrapper.txt

@@ -0,0 +1,18 @@
+HTML.BlockWrapper
+TYPE: string
+VERSION: 1.3.0
+DEFAULT: 'p'
+--DESCRIPTION--
+
+<p>
+    String name of element to wrap inline elements that are inside a block
+    context.  This only occurs in the children of blockquote in strict mode.
+</p>
+<p>
+    Example: by default value,
+    <code>&lt;blockquote&gt;Foo&lt;/blockquote&gt;</code> would become
+    <code>&lt;blockquote&gt;&lt;p&gt;Foo&lt;/p&gt;&lt;/blockquote&gt;</code>.
+    The <code>&lt;p&gt;</code> tags can be replaced with whatever you desire,
+    as long as it is a block level element.
+</p>
+--# vim: et sw=4 sts=4