Config update

Copy fixes from owncloud/documentation#594 and apply them onto config.sample.php

@carlaschroder Have a look at a96f7c1 I added some fixes. Are you fine with them?

cc @PVince81 @wakeup @DeepDiver1975 @LukasReschke 
I meant to update this, it should say "This is a unique identifier for your ownCloud installation, created
 automatically by the installer. Do not change it."