Add comment for each expected_raw_feature indicating CSV source

[leewyang]

This PR adds a comment for each feature in the qualx expected_raw_features list, which indicates:

• the source CSV file produced by the Profiler tool
• the source column name in parentheses if different than the feature name, e.g. _mean features derived from _sum features.
• "N/A", if the feature is derived from other features (or other information outside of the CSV files, e.g. scaleFactor).

The hope is that this list (and the comments) can be maintained as the features evolve.

[amahussein]

Thanks @leewyang
This is very useful indeed!