SingularException during interpolation

[noemiandor]

Certain input birth rate landscapes result in SingularException. Changing the order for the interpolation fixes the issue, for example via: interp = PolyharmonicInterpolation.PolyharmonicInterpolator(X,Y,3) in ploidyMovement.jl. May want to add this as user parameter with a default setting.

[gregorykimmel]

The singular exception was highlighting issues with the interpolator and we will leave as is (with default value set to 2) and not accessible to the user. For now, we will add an extra "more problem-specific" error message.