Add login form to nav bar

When user clicks on "Login" on nav menu, a small form will appear that will allow the user to enter their email & password and log into the site.

By default the mini login form will not show.

![coworflogin](https://f.cloud.github.com/assets/743877/558811/550534f0-c432-11e2-870a-5f630ea5d2c1.png)

(That yellow border you see is just an artefact of loading on Opera)