Add client side validation & refactor new sign up form
(red) Break passing feature test => Signing up displays message
Add capybara-email gem
Add link to set_password email
Rename AppMailer email => set_password to create_password
(red) Write failing routing test => /sign_up_passwords/:id/edit
(green) Make routing test pass => /sign_up_passwords/:id/edit
Rename create_password email to sign_up_password_edit, and fix broken link
(red) Write failing controller test => SignUpPasswordsController#new
(green) Write failing controller test => SignUpPasswordsController#new
Create edit sign up password form
(red) Write failing routing test => PUT /sign_up_passwords/:id
(green) Make routing test pass => PUT /sign_up_passwords/:id