Demo site updates

[isaacwhite]

• [x] Update for new Google credentials options
• [x] Update to make cloud datastore an optional add on step
• [x] Update to account for new oauth creation flow
• [ ] Remove references to team drive in setup docs
• [ ] (optional) make Library work without an oauth provider and include a warning

[isaacwhite]

• [ ] approved_domains needs better description in heroku yaml (should not default to nytimes.com, confusing. See: https://github.com/nytimes/library/blob/master/app.json#L40)