create an actionbar for undo/redo & revert to original

when you edit a photo, pantheon-photos could show an action bar which shows these three options.
That way we could remove undo/redo from the toolbar and "revert to original" from the right click menu.

Launchpad Details: [#LP1406559](https://bugs.launchpad.net/bugs/1406559) swizzle - 2014-12-30 14:56:09 +0000

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The issue names no files, tests, or entry points. First map the existing undo/redo toolbar actions and the revert-to-original context-menu action, then clarify the action bar's placement and behavior with maintainers; done means all three options are available there and removed from their current locations.

Written by the indexing model from the issue text.