Generalize code to retrieve conversion parameters for all example data

[alessandratrapani]

With this PR I wanted to generalize the code for all example data given by the Cai Lab.

Additions:

1. add util functions for retrieving the data source folder path
2. add a util function that update a yaml file that contains the for each subject and each session the list of args to pass to the session_to_nwb function

Improvements:

1. the convert session script works for both example subjects
2. more flexibility in choosing which data stream to add:
   • one can remove the data source path of a specific data stream directly from the yaml file
   • one can choose the data stream to add by simply calling the function for retrieving the data source folder path of that data stream exlusevely

TODO:

• adapt script for converting week session
• adapt script for converting all session