* Adds `view.Workspace.Library` and `view.Workspace.Gallery` as extensions of `view.Workspace` to implement the individual screens
* Shifts the toolbar logic that was library-specific from the generic `Workspace` view to `Workspace.Library`.
* Adds a toolbar to the `Gallery` view.
* 'Create a gallery' and 'Return to media library' buttons toggle between the two views.
* 'Insert gallery into post' closes the modal, but does not actually perform its namesake action.
* Note that elements can still be deselected in the gallery view. This will be fixed in a future commit.
Improvements to avoid over-eager event unbinding:
* `Modal` views now properly detach their contents before replacing them with a new element.
* Likewise, `Workspace` views detach their main content blocks when re-rendering the view.
To test the gallery workflow (which is incomplete), run the following in your browser's console:
`wp.media({ multiple: true });`
see #21809, #21390.
git-svn-id: http://core.svn.wordpress.org/trunk@21906 1a063a9b-81f0-0310-95a4-ce76da25c4cd
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