Updating figures.

Changing all fonts to a light version of Helvetica neue (however that is
supposed to be pronounced).
Changing colour schemes (to reflect within-segment lineages) in both
lineage ratio figures and `RailroadPlotDated.pdf` and adding
same-coloured bars to `InfB_genomeGrid.pdf`.
Adding robust counting results to supplementary materials - can't see
anything glaring worth mentioning in the manuscript.
Also flipped y axis on `InfB_betweenDiversity.png` (fixes #6). Might
have to run PB1 and PB2 trees with traits the right way round, since the
figure should then have small drops in diversity before 1997 and then
recover.