Quick and dirty implementation of WicketAtmosphereTester
Atmosphere tester - write to the http response (doesn't work)
Fix the atmosphere behavior listener interface's type
Rename WicketAtmosphereTester to AtmosphereTester

Start the page after configuring AtmosphereTester/TesterEventBus so the method collector is called for all components in the page
Expose TesterBroadcasterFactory as BroadcasterFactory#getDefault()
Fix the callback url to the AtmosphereBehavior. It should be an Ajax one to prevent incrementing of the page id/renderCount
Pretend being a websocket request when using AtmosphereTester
Upgrade Atmosphere to 2.1.8
Make it possible to write to the underlying http response
Pretend it is WebSocket connection
WICKET-5674 Use jquery.atmosphere.js as a Webjar
WICKET-5674 Use jquery.atmosphere.js as a Webjar

Use IInitializer to setup webjars and not bother the developer to do it manually
Remove custom executors - they are no needed because of TesterBroadcaster#executeBlockingWrite(AtmosphereResource, Entry)
Add ASL2 headers
Merge branch 'wicket-atmosphere-tester' into 5674-jquery-atmo-webjar
Merge branch 'wicket-6.x' into 5674-jquery-atmo-webjar
WICKET-5674 Use jquery.atmosphere.js as a Webjar