View and View/Entity: IOC event destruction

Event unbinds happen now in View/Entity superclass, View. They happen
through the IOC .stopListening() method, provided by pubsub trait.

This alleviates the reliance on `this._model` in View/Entity. All
subclasses are encouraged to use the IOC bind .listenTo() to establish
binds on their models, or to call the model unbinds manually.

Fixes #60