Fix broken link in dashboard with broken objects

[lukasolson]

Closes #4200.

When you have an object inside a dashboard that links to a no-longer-existent index pattern (or is in some way otherwise broken), the edit link was bad and would send you to a 404 page.

With this change, we link to the object editor in such cases, so you can modify the object. If the object itself has been deleted, the edit link should no longer show up at all.

This PR also removes the Inflection library, because it was only used in one place (to singularize "searches" to "search" etc.) and it wasn't even necessary.

[w33ble]

This LGTM.

There seems to be a lot of custom code in a number of places when using the saved_object_registry though - I wonder if some of the functionality can be moved to that module instead.

Also, if we used an IndexedArray in there, you could get rid of your type mapping stuff and just use registry.all().byType[$scope.panel.type] in the _.find.

[spalger]

Yeah, saved_object_registry is a legacy module we should replace with an IndexedArray or actual Registry someday. Created #4243 to track

[spalger]

Everything here looks good, except that the 'notFound' query string param accepted by the saved object editor is not being utilized. This param displays a message helping the user understand what's going on.

The simplest solution was pretty dirty so I played around and wrote a solution that I think is a little cleaner. @lukasolson sent you a pr lukasolson#5

[spalger]

LGTM!