Fix: PNN model and plot directories

[rbarrue]

If not in debug mode, the PNN models and plots are stored in the top-level directory instead of their versioned directory. This PR fixes this.

Making a PR (instead of just commiting the small changes) so that people are aware, as we'll be having a PNN training round quite soon, and I didn't want people to not know where the trained models are.

[schoef]

Please put the following there. i had fixed that long ago, don't know why it's not in this branch.

model_dir = os.path.join(user.model_directory, cfg_base+("_for_debug" if args.for_debug else ""), "PNN", J["id"])
plot_dir  = os.path.join(user.plot_directory,  cfg_base+("_for_debug" if args.for_debug else ""), "PNN", J["id"])