* Update devise to latest version

* use letter_opener for mails in development
* bring back the flash
* fix redirect loop for logging in
* move all mailer/devise settings to config/config.yml

config/config.yml.example

@@ -1,6 +1,10 @@
 defaults: &defaults
+  # The sender address of emails
+  devise_mail_sender: no-reply@localhost
   # The hostname to be used when building the URL in the emails
   url_for_emails: localhost:3000
+  # A secret key. You can generate one with 'rake secret'
+  devise_secret_key: 12345 
 
 development:
   <<: *defaults
@@ -10,4 +14,3 @@ test:
 
 production:
   <<: *defaults
-