'Insert into post' is the primary action when either one item is selected, or any number of non-image items are selected. If multiple images are selected, 'Insert into post' becomes secondary, and 'Create a new gallery' takes the primary spot.
Adds a method to `get` Button views from the Toolbar. Adds a model for certain button attributes to allow size, style, and text to be easily changed.
see #21390, #21808, #21809.
git-svn-id: https://develop.svn.wordpress.org/trunk@22027 602fd350-edb4-49c9-b593-d223f7449a82
419a03862e