plots a pca on the treatment, seconds, bio-rep
plot_pca.RdPerforms and draws a PCA plot with four panels, PCA with sample names coloured by treatment, seconds and biorep and a scree plot of the PCA dimensions
plot_pca.RdPerforms and draws a PCA plot with four panels, PCA with sample names coloured by treatment, seconds and biorep and a scree plot of the PCA dimensions