COMETD-527 - ServerSessionImpl - doDeliver - concurrency bug on MaxQueueListener notification.

Changed the semantic of MaxQueueListener and now invoking it just before
adding the message to the queue, from within the sync block.
Updated Jetty to 9.2.0.M1.
Introducing notifications for onload and onerror events.
Fixed typo.
COMETD-528 - Update jQuery to 2.x.
Removed debug logs.