Add pole figure contouring

[adigitoleo]

We need contouring of pole figures, like here.

No quick and easy way to do this, need manual counting stations on the circle and the color corresponds to the number of counts "near" the counting station/point compared to the number expected for a uniform distribution.

Then apply smoothing, see here for some examples using linear/exponential smoothing etc.

[adigitoleo]

Rudimentary contouring introduced in #93, very sensitive to kernel smoothing parameter.

[adigitoleo]

Proper contouring depends on ODF, see #113.

[adigitoleo]

https://github.com/vollmerf/spherecontour

[Patol75]

https://vollmerf.github.io/orient/