R1:6a04328430f0

Tighten scope requests with Google OAuth

Summary: We currently make a ludicrously gigantic permission request to do Google auth (read/write access to the entire address book), since I couldn't figure out how to do a more narrowly tailored request when I implemented it. @csilvers pointed me at some much more sensible APIs; we can now just ask for user ID, name, and email address.

Test Plan: Created a new account via Google Oauth. Linked/unlinked an existing account. Verified diagnostics page still works…