Graph Neural Networks

@SidneyLann @partarstu some of the building blocks are there but @SidneyLann is right that it would need some fleshing out. @partarstu could you detail more of what you might be looking for?

Eg: Is there a manual about GCN(Graph Convolutional Networks) using DL4J - #12 by xiumuzidiao
It seems like some folks make it work. I think what @SidneyLann wanted was something higher level. If you’re willing to (sort of like what you did with your other models) I’d be happy to work with you on what is/isn’t supported.