Updated POMs to not reference staging repositories for Jetty 9.1.0, now available in central.
Fixed WebSocket idle timeout to take into account the /meta/connect timeout.

Before, the idle timeout for websocket was too small, leading to connections
being closed very quickly, before the /meta/connect could return, actually
turning websocket into long-polling (on a new connection every time).

Introduced a common Config class that is used by both client and server.