Center Buttons
Center Buttons

Since Version 18.0.0 the Registration button of the [registration app](https://github.com/pellaeon/registration) is not centered anymore.
nextcloud/server,nextcloud/server,nextcloud/server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,nextcloud/server