Email Signups AB test 2.0

Email Signups AB test 2.0
===

This changeset reinstates the Email Signups AB test for the next two weeks with some changes to the test.

![email-inline-alt](https://f.cloud.github.com/assets/1170410/2065357/100b2d7e-8ce0-11e3-8b46-ab22a300f3f4.png)

The changes are;

 - Removed all variants except the previous winning variant `email-signup-left-meta-alt`
 - Allow component to appear to *non-signed in* users.
 - Add sign-in flow with return url for anonymous users.
 - Add local storage detection to hide component from users who are already registered.

Everything else remains unchanged and once this pull request is approved i will fill out the form for AB tests again.

![qwzsote](https://f.cloud.github.com/assets/1170410/2065387/9a8a2ed2-8ce0-11e3-999c-f761437c4df0.gif)