Stale content due to lack of Cache-Control headers (dev server)

[msegado]

The Gobble dev server doesn't set any cache-control headers, which can lead to browsers caching content during development (and some related head-scratching about why the latest changes aren't showing up). Should be easy to fix by adding something like the following to all the server responses:

response.setHeader( 'Cache-Control', 'no-cache' );