Allow mojits to extend YUI modules in other mojits

This pull request allows mojits to easily extend YUI modules of other mojits. For example:

mojits/Vehicle/controller.server.js

```js
YUI.add('VehicleController', function (Y, NAME) {
    var Vehicle = function () {
        this.type = 'Vehicle';
        this.transmission = 'automatic';
    };

    Y.namespace('mojito.controllers')[NAME] = Vehicle;
    Y.extend(Vehicle, Y.Base, {
        index: function () {
            ac.done(ac.params.body('brand') + ' ' + this.getType());
        },
        getType: function () {
            return this.type;
        }
    });
}, '0.0.1', {
    requires: {
        'oop',
        'mojito-params-addon'
    }
});
```

mojits/Motorcycle/controller.server.js

```js
YUI.add('MotorcycleController', function (Y, NAME) {
    var Vehicle = Y.mojito.controllers.VehicleController,
        Motorcycle = function () {
            Motorcycle.superclass.constructor.call(this);
            this.type = 'Motorcycle';
            this.transmission = 'manual';
        };

    Y.namespace('mojito.controllers')[NAME] = Motorcycle;
    Y.mojito.util.extend(Motorcycle, Vehicle);
}, '0.0.1', {
    requires: {
        'mojito-util',
        'VehicleController'
    }
});
```

In this example, the Motorcycle mojit extends the Vehicle mojit, which extends the Y.Base class (extending Y.Base is not a requirement, the example just illustrates multiple level of extensions). Notice that the controllers can be defined as a function; this allows mojits to extend using Y.extend, which ensures that the prototype chain is maintained regardless of how many levels of extensions. Also notice that the Motorcycle controller does not have to re-specify the 'mojito-params-addon' requirement; it just has to specify the Vehicle controller requirement, and its addon will automatically include any addon required by Vehicle controller.

To ensure that mojit dependencies work with resourceStore > lazyMojits on, mojits depending on other mojits should specify their dependencies in defaults.json:

mojits/Motorcycle/defaults.json
```js
[{
    "settings": [ "master" ],
    "dependencies": [ "Vehicle" ]
}]
```
The new Y.mojito.util.extend method is a wrapper around Y.extend, which allows the r/s arguments to be either functions or the usual object literal used for controllers/mojits/binders.