`wp.media.model.Query.more()`
* If a request has already been sent out for more attachments, return that request object instead of creating another.
`wp.media.controller.Region`
* A region allows views to be swapped in and out of a section of the page without either view having to know about the other.
* Application components can use the same callbacks and resources by leveraging `Region.mode()`, which triggers a set of callbacks to create or transform the current view, but only if necessary.
`wp.media.view.Frame`
* Leverage `Region` controllers instead of forcing states to swap view objects, which causes states to fit more comfortably in the controller-camp.
* Add `previous()`, a method to fetch the previous state `id`.
* Separate out the default settings over several objects (so blank frames can be instantiated).
`wp.media.view.MediaFrame`
* The base `Frame` used for media management: handles integration with the `Modal` and `UploaderWindow` views.
`wp.media.view.MediaFrame.Post`
* Includes all default media states and callbacks necessary for inserting media into a post.
see #21390.
git-svn-id: https://develop.svn.wordpress.org/trunk@22437 602fd350-edb4-49c9-b593-d223f7449a82
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