Pole sampling using van Mises Fisher distribution for orientations

[Leguark]

@flohorovicic we should invite Evran to our repository so I can assign it to him

[Leguark]

for Lihuan

[alex-schaaf]

added class gp.utils.input_manipulation.VanMisesFisher in my development branch with method .rvs(size=n) for sampling to mimic scipy.stats distributions (for my ABC stuff). this will not work with pymc though

[elimh]

I figured out how to sample from the vMF distribution using pymc2 and can add a tutorial notebook (like ch. 3 but for orientations) soon. In the long run it would be cool to solve problem #2458 of pymc3 so that the vMF distribution can be used directly in pymc.

[Leguark]

Is this just waiting for a test?

[AlexanderJuestel]

This may be related to #475, maybe we can solve both at some point together