Fix the automatic gui detection + introduce argparse for argument parsing

I fixed the GUI detection, which was matching GNOME all the time.
Also, I used argparse to allow the user to specify the language, gui, verbose and selection mode.
Note that this makes the version for the terminal unable to handle more than one file at a time. 
The fix for this would be to loop the main() for each file in the args, but for now, it fits my usage so I don't mind.
Next time maybe