Feature: Use custom functions to send authentication emails

[benfurber]

Is your feature request related to a problem? Please describe. While we have a lovely email templating system now ('functions/src/emailNotifications') when users sign-up or need to reset their password, they got a boring basic text email - the horror. This is because the authentication related messages use the default firebase flow.

This is important because we like the platform to be exciting and it's just a boring introduction to being a member to get that plain text message.

Describe the solution you'd like Using a cloud function, link up the authentication messages with our templating system.

[thisislawatts]

To configure your Firebase auth templates you can find them under:

• Open your project in the Firebase console.
• Go to the Email Templates page in the Auth section.