Add a password strength indicator to SIGN UP and PROFILE pages

Fixes #1647

Added a password strength indicator to the sign up page. You can see how it looks in the following screenshot. In the sign up page, it checks if the password contains the username and alerts the user about it. If the user still wants to proceed with creating his account, nothing will stop him. This is merely a message. The indicator changes the input background color based on the strength like this:

![new_full](https://dev.gitlab.org/uploads/gitlab/gitlabhq/0e6da27cfe/new_full.png)

The password strength indicator can also be found in the profile edit page. It functions in almost the exact same way, with the exception that it doesn't check if the password contains the username.

![edit_full](https://dev.gitlab.org/uploads/gitlab/gitlabhq/f73001539e/edit_full.png)

There are tests included.

/cc @job

See merge request !1227