Add TERTp into Fig S5

[sjspielman]

Closes #1654

This PR updates the S5 figure script to highlight points with TERTp mutations of interest.

Here are the new figures:

supp_terc_normextend.pdf supp_tert_normextend.pdf

[sjspielman]

This script does not go through CI, so we can merge before checks are complete.