Add support for Appetizers

[peterkos]

(or, as some call them, "App Clips")

We'll need to do some brainstorming on how exactly they would be implemented -- what screens we want to show, etc.
As per this WWDC session:

• Custom URL callbacks are not supported for authentication [in App Clips], use ASWebAuthenticationSession instead
• If user downloads the full app from the app clip, iOS auto-authorizes camera, mic, and bluetooth permissions

Either way we should look into implementing Sign in with Apple (per @cbaudouinjr) but I'm not sure how that would integrate w/ our questionnaire system.