Create python utility library to work TVB exported data

This issue concerns two tasks:

+ create a demo that reads an h5 file downloaded from TVB (eg, TimeSeries) to expose the keyvalues we use to store the relevant pieces of data.

+ create a reader for a datatype group (useful if I want to reconstruct the PSE figures or aplly another analysis in a collection of TimeSeries) (see also TVB-994)