Update plot_features.py example to use fst
Update plot_features.py example to use fst

Unclear whether this example still works. It is coupled to
synthesis configuration file formats, and there have changed
a few times.

lidakanari/NeuroM,wizmer/NeuroM,BlueBrain/NeuroM,liesbethvanherpe/NeuroM,mgeplf/NeuroM,juanchopanza/NeuroM,eleftherioszisis/NeuroM