Trigger browser password manager after sigining up

When the user will submit sign-up form/modal, he/she will be redirected to this page:

![screen shot 2014-09-23 at 23 37 38](https://cloud.githubusercontent.com/assets/5732281/4377567/1618832a-4350-11e4-9f26-131fe8c4d234.png)

and the browser's password manager will be triggered, offering user to save username/pasword.

cc @eviltrout