Implement built-in templates for "new project"

[eleanorjboyd]

Templates should include the following:

• flask
• fastapi
• django
• python package
• python script
• (confirm everything works with conda)

make sure "Create Project" is a command available in the command palette

[eleanorjboyd]

as follow up: http://github.com/microsoft/vscode-python-environments/issues/305