Add a banner when the site is in the Dev, Preview or Staging environment

The banner is pretty simple, see attached image. It depends on a CSCFG setting "EnvironmentName" which can be "Production", "Staging", "Preview", "Development" or empty (which is treated like "Development". There are messages for each environment. If the environment name isn't recognized, no message is rendered.

Fixes #207 

![Environment Banner](https://f.cloud.github.com/assets/7574/181239/6ae1e984-7c49-11e2-8560-3a3506473499.PNG)