Transfer function editor in Jupyter Notebook

Just created a Jupyter Notebook widget for volume rendering with Brayns. Also improved the volume rendering module for better performance and image quality.

Install it with:

pip install ipyTransferFunction

The code sources are:
Transfer Function: https://github.com/favreau/ipyTransferFunction
Brayns: https://github.com/BlueBrain/Brayns
Volume rendering module: https://github.com/favreau/brayns-research-module