Implementation of jep #65

[Hind-M]

Implementation of JEP #65

• [x] Implement JKT tests (PR)
• [ ] Check protocol version in reply and behave accordingly
  • [x] Update jupyter_server (PR)
  • [ ] Update jupyverse?
• [ ] Update protocol_version in Jupyter client and kernels (in xeus for xeus based kernels)
• [ ] Update messaging doc in Jupyter client
• [ ] Update Jupyterlab to add and handle the new iopub_welcome message type
• [ ] Update IPyKernel

[JohanMabille]

:tada: