Implement TreeViz

[jashapiro]

As we start to get more data, we will want more ways for people to potentially interact with it.
TreeViz is a potentially interesting package for visualization, either instead of or in addition to UCSC cell browser #40.

From one of their vignettes:

TreeViz is a package for interactive visualization and exploration of Single Cell RNA sequencing data. TreeViz provides methods for exploring hierarchical features (eg. clusters in single cell at different resolutions or taxonomic hierarchy in metagenomic datasets), while supporting useful data visualization charts like heatmaps for expression or count matrices and scatter plots for dimensionality reductions like UMAP or TSNE.

https://github.com/HCBravoLab/TreeViz