Kernel types too specific

[odunbar]

Issue

CalibrateEmulateSample.jl/src/GaussianProcess.jl

Line 60 in b8338a0

kernel::Union{<:Kernel, <:PyObject, Nothing}

We hope to add new GP packages via adding a new package Mypkg, struct mystruct and the mlt methods (build_models! and predict! etc)
but right now they are also constrained (needlessly ) to type.

Solution

Don't require specific kernel types in the constructor, just pass them into the wrapper.