Change the working dir of scripts to script path

Normally, MDANSE uses absolute paths in the scripts it creates. For tutorials, that's not possible, since we cannot predict where the users will place the files. The current solution of using a relative path and having the users start the script from the correct working directory has shown to be a potential problem.

In the future, we should add a line to every tutorial script which will change the working directory to that where the script is located.