Better rank plot colorschemes for accommodating users with colorblindness

[fedarko]

The sample plot already has various grayscale schemes that should be helpful, esp. when #240 is addressed; but I don't think the rank plot's defaults are all that great. Should ideally do testing with Coblis to try adding new colorschemes (or maybe other methods of "marking" features) and verify that these work ok.

One example I've been messing with is using mostly monochrome colorschemes for the rank plot -- e.g.

Of course, the problem with this is that white bars at the "ends" of the rank plot are basically impossible to see on a white background... hm.