Remove login drop down when Auth views are not registered.

Fixes #1738 

Screenshot show the key view: 

![screenshot 2014-09-02 14 52 58](https://cloud.githubusercontent.com/assets/64686/4118386/6f2bd1da-32a0-11e4-80c1-3b9973bde4d5.png)

Here the user is logged in but the auth views are not registered. 

Tests cover all four corners of the grid (logged in?; auth views enabled?)
We should probably have consistent `<li>` tagging around both `optional_login` and `optional_logout`. May involve moving the `li` inside the template tag for `optional_login`.