View, controller & route action handlers are now expected to be defined on an `actions` object.

The previous locations are now deprecated (i.e. defining action handler functions directly on the view, directly on the controller, and in an `events` object on the route).

This makes action-handling consistent across Ember.

In the proposal and PR process for this change, some developers expressed concern that "actions" was a part of the domain language of their app. To mitigate the impact on these apps, Ember will automatically rename `actions` to `_actions` behind the scenes. This allows an ObjectController to proxy to a model with an `actions` attribute, even if you have an `actions` object defined on the controller.

Actions properties must be defined at extend time. An assertion has been added if you try to define `actions` as part of create in a view, controller, or route.