[FEATURE] Add config and use composer autoloader.

We use composer already to install SabreDAV. Include config
composer.(json|lock) to install and manage more dependencies
in future.
Also provide PSR-4 autoloading for our namespaced classes, e.g.
"Zotlabs\". To regenerate autoloader maps use:
$ composer install --optimize-autoloader --no-dev

We could also remove the whole vendor/ folder from our repository, but
that would need changes in deployment and how to install hubs and needs
more discussion first.

vendor/composer/autoload_psr4.php

@@ -6,6 +6,7 @@ $vendorDir = dirname(dirname(__FILE__));
 $baseDir = dirname($vendorDir);
 
 return array(
+    'Zotlabs\\' => array($baseDir . '/Zotlabs'),
     'Sabre\\Xml\\' => array($vendorDir . '/sabre/xml/lib'),
     'Sabre\\VObject\\' => array($vendorDir . '/sabre/vobject/lib'),
     'Sabre\\Uri\\' => array($vendorDir . '/sabre/uri/lib'),
@@ -15,4 +16,6 @@ return array(
     'Sabre\\DAVACL\\' => array($vendorDir . '/sabre/dav/lib/DAVACL'),
     'Sabre\\CardDAV\\' => array($vendorDir . '/sabre/dav/lib/CardDAV'),
     'Sabre\\CalDAV\\' => array($vendorDir . '/sabre/dav/lib/CalDAV'),
+    'Psr\\Log\\' => array($vendorDir . '/psr/log/Psr/Log'),
+    'Hubzilla\\' => array($baseDir . '/include'),
 );