Enhance analysis command

[ravih18]

#258:
"Must become diagnosis independent (is now meant to work on AD, CN, MCI...).
Also it was made to work on specific dementia scores (MMSE and CDR) which are handled specifically as they can be either continuous are discreete.
Maybe instead the user could give the set of discrete or continuous values they want to integrate in the analysis.
We can also rely on pandas to automatically detect which columns correspond to continuous values or discreete values."

More generaly it would be great to define what kind of data analyse are always performed and provide and efficient tool to return the results based on the new organisation provided in #312 and #314.

For instance, this command would return the statics of all the metadata in each split, and the general information over the dataset.