Bnlearn

* added library requests

* Fix for import examples (requires latest numpy version)
* replaced wget with internal python function.

* Added cdn resources to fix interactive plot in jupyter notebook and Colab

* Fix for interactive plot. It did not show up correctly but now it does again.

* `sklearn `is changed to `scikit-learn` in the setup and requirements (issue 66 )

* plot function `bn.plot(model)` return figure axis.
* Setup file contains import of `python-louvain` instead of `community`
* docstring updates regarding this output.

**Example:**

model = bn.import_DAG('sprinkler', CPD=True)
df = bn.sampling(model, n=1000, methodtype='bayes')
fig = bn.plot(model)
fig['ax']