WIP: Draft of new UI layout
Rename App.Model -> App.Zipper
Extract Outline.Document
Make Action.Result.Update take a zipper
Make Action.Result.Split take zipper-like values
Revert "WIP: Draft of new UI layout"

This reverts commit 27e58819422d40369751cfd5ab74ae5723aa893a.

Conflicts:
	App.elm
Change Action.Result to take value, zipper type parameters instead of value, cursor
Action is now (v,c) -> Result instead of v -> c -> Result
Inline Core.String.Cursor
Replace Core.String.render with renderValue/renderZipper
Update type signatures in Core.String to get rid of Core.Action
Inline Core.Action.Action
Define Core.Array.Zipper
Rewrite Core.Array.Zipper to use an actual zipper data structure
Huge refactoring to convert Outline.Entry to use zippers