Create sign-up, forgot password emails etc

[carlnewton]

Create sign-up, forgot password emails etc

[carlnewton]

This should also handle existing email addresses because that isn't currently dealt with. It's important that the user signing up does not get a different experience when using an existing email address to prevent email address harvesting. This can be handled in the verification email. e.g. "Welcome to Habitat" vs "Someone attempted to create a new account with this email address, did you forget your password?"