Strictly hierarchical assertions preceding fit method

[kdgutier]

• Deprecates pandas tags leaving pure numpy in methods.py and probabilistic_methods.py
• Saves unnecesary computation to failed run after some fit time spent.

[elephaint]

First is in place.

Second we could add a class attribute IS_STRICTLY_HIERARCHICAL that can be checked in reconcile, but it's a minor thing imho (in time).