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 
Maybe we should keep what this is?

~~~
Loglevel to start logging at. Valid values are: ....
~~~