Add open house message below header

This adds an open house message (and registration button) to the website.

Screenshot:

![screen shot 2013-12-07 at 2 38 05 pm](https://f.cloud.github.com/assets/808159/1699321/8db03354-5f91-11e3-86a5-aac6acfe639a.png)

/cc @crabasa