web server extenstion updates

## Updates to the web server

- adding a `callback` param will only convert the response to JSONp (`application/javascript`) if the header would have still been `x/json`
- if the header isn't `application/json` or `application/javascript`, the server will no longer attempt to `JSON.stringify` the `connection.response`.  
  - This means you can manually create XML, Plain Text, etc responses as long as you also change the mime (IE: `connection.rawConnection.responseHeaders.push(['Content-Type', 'text/plain']);`)
- internally traded `connectionHasHeader()` for `extractHeader()` which will return the most recent header of a given name