Upgrade core/webserver to Jetty 7.x

Hi Dan,

While adding Startjava for ISIS-537 I noticed that webserver also uses Jetty 6.x so I've upgraded it.
Please check my changes.

I was going to use Jetty 8.x but it needs Servlet 3.0 and this clashes with Geronimo's dependencies. Since I'm not sure what are they used for I decided to use Jetty 7.x