Rsconnect-jupyter

- pip is now invoked with `python -m pip` instead of looking for the pip executable
- Always use `pip freeze` instead of pulling in requirements.txt.

Changelog
- Renamed plugin from `rsconnect` to `rsconnect_jupyter`
- Publish notebooks with source allowing them to be rendered on RStudio Connect.
- Note: `pip` and `virtualenv` are used to determine dependent packages.
- Deploy logs are shown while notebook is deployed.

- initial release
- publish notebooks as static documents