Notifications are for all windows

[woolie]

All notifications are being listened to no matter the scope. I moved away from the C++ observer architecture that was in the Chrome codebase as I wanted this to be a pure Objective-C codebase.

The listeners need to be able to filter the notifications so that they do not act on notifications not meant for them.

The symptom of this is:

• Create a Window,
• Create another TAB
• Tear off the second TAB to another window

The new window has the torn off tab, but there is a phantom one in the old window.