Add support for dtreeviz visualizations

[mepland]

Add any required translation code to allow imodels trees to be plotted with dtreeviz. This basically boils down to successfully generating a ShadowDecTree object from an imodels tree.

We can reuse the existing ShadowSKDTree constructor by converting imodels trees into sklearn objects, then calling:

sk_dtree = ShadowSKDTree(tree_classifier, X, y, features, target, [0, 1])

Alternatively, we can make an imodels specific implementation of ShadowDecTree, similar to the sklearn implementation here, but that may be more work than necessary.