Update the JB, data, dataset_description.json files

With this PR I fixed the requested as comments in this PR

A friends_util.py module created to curate all the execution of the estimations.
- Dependencies are cleaned and moved to the friends_util.py module.
Data is cleaned.
Descriptive text is added to the JB.
Notebook is shortened.
Bug in the ngram plots are fixed.
Clean run of the notebook is provided.
dataset_description.jsonis renamed.
the numerical data in dataset_description.json converted from str to int.

courtois-neuromod / friends.stimuli