Relative paths in the configuration

Original request from Frederik:

For the 'mask file' that has been added to the run_config.yml file: would it be possible to make this path relative to the output_folder instead of the proposal_folder (similar as for the poni_file)? I created a mask file using pyFAI for this experiment and the output folder seemed the most logical place to put it.

Perhaps there are other like this. Allow absolute paths?