Add capability to support configuration

[jasonzhang0413]

We are leveraging this project to easily set up web socket server end point. We have found the connection between web socket server and client will automatically drop when there is no activity for five minutes. The five minutes is the default idle timeout setting in jetty web socket implementation. We are required to make the persistent connection once the connection is established. Connection dropping means something goes wrong on either server or client side. We want to prevent this automatically disconnect by introducing configuration.
Please let me know if this is considered a valid request.

[coveralls]

Coverage decreased (-2.6%) to 80.583% when pulling ecf75bd on jasonzhang0413:master into b3695a8 on LivePersonInc:master.

[black-snow]

looks good to me

[zuozhiw]

In case anyone is wondering the same question, here's my solution:

Add the following code inside the run function provided by dropwizard

WebSocketUpgradeFilter webSocketUpgradeFilter = WebSocketUpgradeFilter.configureContext(environment.getApplicationContext());
webSocketUpgradeFilter.getFactory().getPolicy().setIdleTimeout(100000);
environment.getApplicationContext().setAttribute(WebSocketUpgradeFilter.class.getName(), webSocketUpgradeFilter);

you can also easily set other configurations after getPolicy()