Create a subpopulation report

[shntnu]

The following RMD file contains the code to produce the PDFs containing the images of subpopulations which are enriched or de-enriched in a treatment.

https://github.com/carpenterlab/2017_rohban_elife/blob/master/code/Cluster_Interpretation.Rmd

Right now it is not structured enough and also not independent of how the single cell data should be accessed. In this issue we intend to fix those dependencies.

[shntnu]

#107 implemented subpopulations. This issue is about using that to create a report.