support custom modules in output dir

[jabooth]

Currently we aren't too careful about the naming of everything in the output directory. If a user runs an experiment with lots of custom modules (e.g. custom dataset, custom lm_processing, custom methods, custom normalisation results) we currently will just hit strange errors in the output. I had a little go at ensuring these problems would be mitigated at least for the error_name here:

        name = '{}_{}'.format(i, Path(error_name).name.replace('.', '_'))

but clearly this requires deeper thought to work for all modules.