style(rxApp): Change colors for pre-prod menu

Closes #538 

When a product is in the `preprod` environment (i.e. `https://preprod.encore.rackspace.com`), put a warning banner on the top of the screen and change the nav menu colours.

This PR also adds the `preprod` environment. Before, we had `unified-preprod`, which means "anything that's not `production`". We still have that, but `preprod` is now its own identifiable environment.

![screen shot 2014-09-24 at 2 57 27 pm](https://cloud.githubusercontent.com/assets/9376/4394050/9e97b748-441d-11e4-9858-b530f16e3e8c.png)
Maybe convert these colors to vars and put in the vars.less file? I'm torn on whether it's worth the effort.