Revisions: Move data management into the frame state. See #24425.

This helps to solidify the separation between data and UI. We track the diffId internally now, as the property itself was never referenced, and was always derived from the 'from' and 'to' models. This also sets us up for better request debouncing and diff management.



git-svn-id: https://core.svn.wordpress.org/trunk@24609 1a063a9b-81f0-0310-95a4-ce76da25c4cd