[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/sabre/vobject/bin/generateicalendardata.php

@@ -29,7 +29,7 @@ include __DIR__ . '/../vendor/autoload.php';
 
 fwrite(STDERR, "Generating " . $events . " events\n");
 
-$currentDate = new DateTime('-' . round($events / 2) .  ' days');
+$currentDate = new DateTime('-' . round($events / 2) . ' days');
 
 $calendar = new VObject\Component\VCalendar();