change the default color map used for icicle plots

[trontrytel]

I was thought recently that "rainbow" colour maps should be avoided at all times. (They can be even harmful) There is a nice talk about it at SciPy Conference:
https://www.youtube.com/watch?v=xAoljeRJ3lU.

Both Python and Matlab recently changed their default colour maps from "rainbow" to something better. The new default for Matlab is https://bids.github.io/colormap/images/screenshots/parula.png. For Python see the whole discussion at https://bids.github.io/colormap/

I think it would be good to change the default colour scheme we use in our quick looks from icicle and other models.