Update interaction plot to use new cancer group palette

[jaclyn-taroni]

⚠️ downstream of #1193 and #1196

Working towards PDF versions of individual panels in directories figures/pdfs/<figure number>/panels using the new color palette in #1193.

This is regarding Figure 3 (placeholder image). Here I am:

• Saving the interaction-plot figures for all disease types as PDFs, instead of PNGs
• Removing any labeling of panels by patchwork
• Adding patterning to the stacked bar chart because without it it's a little difficult to distinguish between DMG, CRANIO, and HGG astrocytoma
• Copying over the PDF instead of the PNG (see point 1!)

[jharenza]

The colors look better to me!

[jaclyn-taroni]

The patterning has been removed, as we've updated cancer group colors such that distinguishing between adjacent cancer groups in the stacked bar plots is less of a concern.