Use neurom.fst module in morph_stats app
Use neurom.fst module in morph_stats app

Simplifies code and speeds up execution.
Fixes population stats which were completely broken.

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