Added plot showing sorted eigenvectors

[hdrake]

I added a few lines so that users can see how to plot (in grid space) the eigenvectors with the lowest/highest growth rates.

It took me a while to figure out the new set_state method API that requires specifying the subsystem in addition to the index, so I thought it would be useful to include it in at least one of the EVP examples.

[kburns]

Thanks!