Create sign up email verification with links

[plinck]

When a users signs up, make them verify their email so I don't get everyone and their brother signing up for my app and prevent spam and trolls:
See: https://firebase.google.com/docs/auth/ios/email-link-auth

[plinck]

In branch signUp on 2/8, I Added ability to send a verification email from contentView. Need to check it and prevent them from using things of not verified.