GFS example notebook seems out of date

[tom-at-rewbi]

The GFS example notebook seems to be unrunnable. It uses imports that are actually within the herbie package (e.g. toolbox is herbie.toolbox) and not global imports, and it also refers to things that apparently no longer exist (from paint.standard2 import cm_tmp -> herbie.paint does not have a standard2 module, nor is cm_tmp in herbie.paint).