* Add cloud function to get custom token from API auth
* Use custom token to authenticate Firebase SDK on server
* Make sure getcustomtoken cloud function is fast
* Make server auth code maximally robust
* Refactor cookie code, make set and delete more flexible
* Set a cookie with an up-to-date Firebase ID token
* Implement server-side authentication cookie reading logic
* Change index page to redirect for authed users
* No branch necessary for logged in users on index page
* Add helpers for creating server-side redirects
* Add some common sense redirects
