Switch from binder to colab

[lgeiger]

We currently allow users to run notebooks on Binder. Unfortunately the Docker build takes quite some time which is discouraging.

I think we should switch to https://colab.research.google.com/ which has support for GPUs or we invest time in pre-building a Docker container to speedup Binder.

We should also integrate some of the content in https://tiny.cc/ucl-bnn