Create callbacks for visualizations

[raghakot]

Create keras callbacks to generate visualizations while training in keras. It would be pretty neat to have:

• Tensorboard callback to push visualization images of choice every_x epochs of training.
• Write them to some output directory.

This could be especially useful when paired with saliency maps or class activation maps

[YaroslavSchubert]

+1

[Abhijit-2592]

+1. when will it be available?