implementation of Backbone mixins

 With Cocktail, it is possible to break out a shared Backbone.js
 model/collection/view behaviors into separate modules and mix them into
 classes with. Cocktail is an implementation of Backbone mixins. Mixins are
 simply bare-bones JavaScript objects that provide additional functionality to
 Backbone objects. Think of them as bags of methods that will get added to all
 instances of objects.