Investigate using ggplot2 heatmap plotting for alpha diversity

[erictleung]

@rnoronha00 is working on adding a heatmap of abundance measures over all samples to get a bird's eye view of the diversity among samples. It is implemented using a standard heatmap package.

To make use of ggplot2's plotting capabilities and to make it consistent with the other plots shown in the application, we can try out using ggplot2's geom_tile

https://learnr.wordpress.com/2010/01/26/ggplot2-quick-heatmap-plotting/