Make model namespace consistent

[chinadragon0515]

Now, when user wants to extend a model based on model builder from EF, he needs to use low level ODL lib code to extend the model, we want to make it easier, make ODataConversionModelBuilder accept an existing model, tracked with issue OData/WebApi#755

Also when user wants to add some new entity type and entity set, and these entityset and type are used by operation, the model extend will need to overwride some existing logic.

Need to make this part model simpler.

[chinadragon0515]

Fix namespace issue too, container will use "default" as namespace.

[chinadragon0515]

code merged. close the issue.