Remove "showProperties" command.

Firstly, it's more of a debugging thing than something that should be
exposed as a command to users. Secondly, it's not very useful, as all
the groups and artifacts can have different properties.

Change-Id: I4aec83550c2f8e597752a181437e580622a6a587
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>