Change the working dir of scripts to script path

[MBartkowiakSTFC]

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.