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.AllowedCommentsRegexp.txt

@@ -0,0 +1,15 @@
+HTML.AllowedCommentsRegexp
+TYPE: string/null
+VERSION: 4.4.0
+DEFAULT: NULL
+--DESCRIPTION--
+A regexp, which if it matches the body of a comment, indicates that
+it should be allowed. Trailing and leading spaces are removed prior
+to running this regular expression.
+<strong>Warning:</strong> Make sure you specify
+correct anchor metacharacters <code>^regex$</code>, otherwise you may accept
+comments that you did not mean to! In particular, the regex <code>/foo|bar/</code>
+is probably not sufficiently strict, since it also allows <code>foobar</code>.
+See also %HTML.AllowedComments (these directives are union'ed together,
+so a comment is considered valid if any directive deems it valid.)
+--# vim: et sw=4 sts=4