Fix tag updating on model save in editor controller

closes #3131
- create a hook in the editor controller that fires on a model's save events
- use this hook to perform all the things that need to happen on save, regardless of where the save originated
- remove logic from instances of model.save() that now belongs in the modelSaved hook
- detach the model event listeners on willTransition in the editor routes
If it's not a property, `controller.modelSaved` works just as well eh?