Updating most figures, adding new supp ones.

Updating all figures with (hopefully) their latest versions. Changes are
either the M1-MP/NS1-NS issue or colour scheme updates. I didn't update
some, since I'm re-running some trees due to labeling issues.
Also adding a lot of supplementary figures relating to exact-approximate
SPR distances. Basically showing that approximate SPR distances are
reasonable overestimates of exact SPR distances.