New hooks for external integration to notification intiialization

Adds two new hooks to allow extensions to tie into the notification
loading process.  Between these two hooks and the new isInitialized()
method any extension can run code whenever a notification is displayed.

Change-Id: If351835be5f65ca098e2d235ea8c8e4dc40ae2b4
Merge "New hooks for external integration to notification intiialization"