Disable X-Powered-By header and fix express.bodyParser() warning.

* Disables the X-Powered-By header without middleware.
* Replaces express.bodyParser() with express.json() and express.urlencoded(). This removes a warning from connect.

>  connect.multipart() will be removed in connect 3.0
>  visit https://github.com/senchalabs/connect/wiki/Connect-3.0 for alternatives
>  connect.limit() will be removed in connect 3.0