Integrate keras-vis visualizations when user is using Keras

[rhsimplex]

One of our paper reviewers points out keras-vis, which we failed to cite. We ought to integrate it into Picasso. Depends on #16 (these visualizations will only be available when using Keras).

[SankBad]

Hey @rhsimplex,

I am trying to integrate grad-cam visualization from keras-vis into Picasso, have you made any progress on this.