Hook call for autosetup.php at the end of successful installation

The core/setup.php after successful installation of ownCloud (when DB already created) checks for config/autosetup.php file and executes it if there's such a file. In config/autosetup.php the one can put instractions needed to tweak ownCloud server after intallation. This is implementation for our https://github.com/syncloud/owncloud-setup/issues/14

This contribution is MIT licensed.