Some cleanup

Hi Torsten,

I made some adjustments, and just wanted to bounce it by you to see if you agree:
* Having cmd-line flag influence the GUI preferences feels a bit weird. Apart from making the core feature class aware of the GUI, it also makes the GUI code more complex. To simplify things, I reverted that behaviour to keep GUI and cmd-line separate. Not 100% sure about this, but it feels simpler, which is a good start :)
* I added the cmd-line flags to the concat test so that the test will pass
* Some minor adjustments