Perf improvements to starting Jupyter

[DonJayamanne]

Options for improving startup performance of Jupyter

1. Start Jupyter as soon as notebook is opened
2. Perform necessary searches (search jupyter, notebook, kernels, etc) eary on. I.e. do the heavy lifting early on, then just start jupyter with everything we have.
   • Do this when notebook is opened
   • Do this if a notebook file exists in workspace (probably long term).
3. Ship jupyter with extension Ship our own Jupyter to eliminate configuration problems #1131
4. Ship nbconvert with extension (small python package).
   • Avoids having to look for it, we can use our copy
   • Or use our copy only if not found locally in current environment (avoid looking for it)

[DonJayamanne]

Closing in favour of https://github.com/microsoft/vscode-python/issues/8217