R Kernel + Externalize notebooks

In this release, your Jupyter Lab is endowed with new features:

• 😮‍💨 Support for R Jupyter Kernel
• 2 new Jupyter Lab extensions:
  • 🚀 git : you can now git commit and push any notebook into an external repository
  • 🎸 deck: you can now turn your notebooks into revealjs like powerpoint presentations