Release 6.20.1: transport.properties has to be moved form groupware to common folder

[changerequest]

The configuration file transport.properties has to become a common property file, that is shared between open-xchange-admin and -groupware processes.
In future releases it can be found in the /opt/open-xchange/etc/common directory, while in the past it was placed in /opt/open-xchange/etc/groupware.