Add radial-distance-layout for plotting dendrograms

[izaakm]

The standard dendrogram ("flat layout"?) is hard to read when there are many genes. Try a 'radial-distance-layout' (i.e., using polar coordinates) instead. E.g.:

• https://github.com/benmaier/radial-distance-layout
• https://stackoverflow.com/questions/51936574/how-to-plot-scipy-hierarchy-dendrogram-using-polar-coordinates