"collection:unchose:one" event should be fired when you choose a new model in SingleChooser #9
Description
Right now in SingleChooser when one calls collection.choose(model), the previously selected models are removed from the @Chosen array, but the "collection:unchose:one" event is not fired for them. And if the BackboneChooser is not defined on the model then even the "model:unchosen" event is not fired. One really needs to keep a track of the unchosen models as well.