Issue #6: ADD email confirmation

app/controllers/v1/sessions_controller.rb

app/controllers/v1/users_controller.rb

app/mailers/application_mailer.rb

app/mailers/email_mailer.rb

app/mailers/user_mailer.rb

app/models/user.rb

app/views/layouts/mailer.text.erb

app/views/user_mailer/email_confirmation.html.erb

app/views/user_mailer/email_confirmation.text.erb

app/views/user_mailer/welcome_email.html.erb

app/views/user_mailer/welcome_email.text.erb

app/views/users/confirmations/new.html.erb

app/views/users/mailer/confirmation_instructions.html.erb

app/views/users/mailer/email_changed.html.erb

app/views/users/mailer/password_change.html.erb

app/views/users/mailer/reset_password_instructions.html.erb

app/views/users/mailer/unlock_instructions.html.erb

app/views/users/passwords/edit.html.erb

app/views/users/passwords/new.html.erb

app/views/users/registrations/edit.html.erb