* Also moves most of the `Frame` view's `createSelection` method to a real `Selection` model (which inherits from the `Attachments` model).
* Properly assigns the library within the `Gallery` state, allowing for the `Gallery` state to inherit from the `Library` state.
see #21390.
git-svn-id: https://develop.svn.wordpress.org/trunk@22323 602fd350-edb4-49c9-b593-d223f7449a82