I updated my post and added some more information. I will try to set this up as explained in the next days. But i think it should work like that.
The thing had an additional comma after autorun=true. It did not provoke errors when i used it like that but now it does. I just removed the comma and all formating so it is one line. And the error was solved.
The sitemap file has to have the same name as the sitemap in the file.
To find out which user you have to add to the gpio group just search who owns openhab by executing following ps command. I think no additional editing of sudoers should be required.
ps -ef | grep open
openhab 424 1 0 18:31 ? 00:00:00 /bin/bash /usr/share/openhab2/runtime/bin/karaf server
...
Is the user openhab or openhabian?