Fix Clusters so that they are allowed to contain Clusters

[drawkward]

When describing what was desired for hclust, it was noted that the end result would be a cluster of clusters (which could be unwrapped like a tree). However, the Cluster type only accepts FeatureVector types as values. We need to be able to cluster together one or more clusters in order for hclust to return the desired result.

[mtabor150]

It shouldn't be a cluster of clusters, it should be a binary tree where every leaf is a feature vector and the nodes are the centroids or other method of distance between the subtrees.

[Kevin-Damazyn]

It should return something like this Note: the picture is huge! zoom out or scroll to the left until you see color. :)

[mtabor150]

Here is the link to Dr. Scannell's blog-post about that image.