Add plotting functions for hierarchical models

[jdehning]

Possible plots: - For one variable: the name of the regions as y axis, x-axis are CI intervals - For each region, table of histograms, one histogram/pdf per variable, like in the paper, eventually up to 3 regions per figures

[pSpitzner]

started a new plot.py module, keeping the old one around for now dc6563504f0ac3f1735e7ac24e5373d008f05bc9