Email Verification + Google / Github SSO for Web

[matthewwong525]

• Sending emails and it's bouncing because email is not verified. Add email verification! Basically after they sign up, change to sign in and shoot a dialog telling user to verify their email.
• Ensure to only send emails to verified users! So maybe if email_verified_at is not null. or something along those lines. (double check that this works with SSO)
• Update UI so that it optimizes for using SSO (effectively hiding the email form). The goal is to drive more people to use SSO because it is better.
• Update docs to teach people how to do SSO or at the very least remove the construction stuff in the README

Will NOT DO:

• Add SSO for Android + iOS #35

[matthewwong525]

Doing this because:

• Unverified emails affect email deliverability and it's key to have good deliverability so emails don't hit spam
• SSO is easier for the user and increases conversion rate!