Include sync as a standalone composer package

[netandreus]

Describe the bug Now we can not use libremail/sync as a standalone package because of this errors:

PHP Warning:  require(/var/www/mailsync/current/vendor/vendorname/sync/vendor/autoload.php): failed to open stream: No such file or directory in /var/www/mailsync/current/vendor/vendorname/sync/sync on line 48
PHP Fatal error:  require(): Failed opening required '/var/www/mailsync/current/vendor/vendorname/sync/vendorname/autoload.php' (include_path='.:/usr/share/php') in /var/www/mailsync/current/vendor/vendorname/sync/sync on line 48