Add pca_plot   - Create princomp object   - Plot first two components colored by cluster
Add pca_plot
  - Create princomp object
  - Plot first two components colored by cluster

catterbu/receptormarker,daniel0128/receptormarker,daniel0128/receptormarker,catterbu/receptormarker,daniel0128/receptormarker,daniel0128/receptormarker,daniel0128/receptormarker,catterbu/receptormarker,daniel0128/receptormarker,nsh87/receptormarker,daniel0128/receptormarker,nsh87/receptormarker,catterbu/receptormarker,catterbu/receptormarker,nsh87/receptormarker,nsh87/receptormarker,nsh87/receptormarker