Added a start page for the extension. Launched in experimental mode such that it opens to new users or when there is a new release. It can be disabled with the setting 'Python: Show Start Page' and it can be opened at any time with the command 'Python: Open Start Page'.
Removed python.jediEnabled setting in favor of python.languageServer. Instead of "python.jediEnabled": true please use "python.languageServer": "Jedi".
Made the variable explorer in the Notebook editor resizable.