Added all grid columns for the derived ItemsViewerBase classes.

Added 'New' button to the base and hooked to up editor form to allow a new item to be created.
Added a TargetMode enum and property to Behavior to make dealing with the type of target a bit easier.
Changed new editor to hide preview window when it loses focus (and thus prevent a floating preview window hanging around when the user switches to other programs).
When creating a new pony in the new editor, automatically open details once the reload completes.