Add support for Kernels?

[oxinabox]

I'm not super up on SVM kernels,
but it would be swish to have that just work.

@willtebbutt was talking about a package that defines a bunch of kernals in a model agnostic way for use in GPs.
And I understand those are the same kernals SVMs use

[willtebbutt]

For reference, this is the kernel package in question. Not much activity recently because we've all been busy, but would be cool to sort out.

[matbesancon]

@theogf would be cool to make that work out