Clean up notebook for issue #20.
Clean up notebook for issue #20.

`cahnHilliard2.ipynb`:

 - [x] Use `MKSRegressionModel` to show sklearn cross validation
 - [x] Remove `MKSRegressionModel` intro, which is now in
   `filter1D.ipynb`.

davidbrough1/pymks,fredhohman/pymks,XinyiGong/pymks,awhite40/pymks,davidbrough1/pymks