Add models to LDL options

/to @ritch 

1. Use 'models' to specify the dependencies to other models
2. The 'models' property is an object, such as:

var MyModel = modelBuilder.define('MyModel', {}, {models: {
    Model1: 'Model1',
    Model2: Model2
}});

3. The model classes will be injected into the newly defined class as
static properties using the keys from the models option.

For example, we can now reference the models by:
* MyModel.Model1
* MyModel.Model2