This PR adds the feature of CPNotificationQueue.
Cappuccino provides a framework for sending messages between objects within
a process called notifications. CPNotificationQueue objects (or simply notification queues)
act as buffers for notification centers (instances of CPNotificationCenter).
Whereas a notification center distributes notifications when posted,
notifications placed into the queue can be delayed until the end of the current pass through the run loop
or until the run loop is idle. Duplicate notifications can also be coalesced so that only one notification
is sent although multiple notifications are posted. A notification queue maintains notifications
(instances of C¨Notification) generally in a first in first out (FIFO) order.
When a notification rises to the front of the queue, the queue posts it to the notification center,
which in turn dispatches the notification to all objects registered as observers.
More informations here :https://developer.apple.com/library/prerelease/ios/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationQueue_Class/index.html#//apple_ref/occ/instm/NSNotificationQueue/enqueueNotification:postingStyle:coalesceMask:forModes:
Unit-Tests in Tests/Foundation/CPNotificationQueueTest.j
