create figures to address research questions

[raynamharris]

During meetings on Mar 12 and 13, we (Matt, Becca, Rayna) decided we wanted to make the following four figures to address the research questions outlined in the README.md

• [x] a PCA showing the relations between sex, treatment, tissue (maybe even include data from previous studies of stress and CORT)
• [ ] a WGCNA plot showing the correlations of gene expression across tissues and with hormones
• [ ] an upset plot showing counts of shared and uniquely differentially expressed genes

[raynamharris]

See #4 for a detailed discussion of progress towards PCA plots