[Feature Request] Improve Errors on Signup Form Validation

[sbmsr]

Description

Our signup form is a bit incomplete. We need to handle 4 cases:

1. successful signup
2. empty email
3. taken email
4. repeat email

The code is in place. We just need you to add some logic to hook everything up.

Expected behavior

The signup form should behave like so:

Successful Signup

Empty Email

Taken Email

Repeat Email