Sign In and Sign Up need to respond to HTTP error code

[ondrae]

Description

We will soon be returning the correct error codes from the backend. We'll need to watch for these codes and display the correct alert to the person trying to sign up or in.

To Reproduce

Go to http://staging.bizfriend.ly/signin.html and try to sign in with garbage info.

Tips

• [x] After a failed signin, check your console. In the object.responseText we can see the message we want to display
• [x] Populate #signin-feedback and #signup-feedback with these error messages.