Commented Issue: Depend upon abstractions instead of concrete implementations for instancing Edm* types [1178]

For example, EdmEntityObjectCollections constructor takes a IList<EdmObject> instead of a List<IEdmObject>. This limit the ability for third parties to provide their own untyped implementation.

Review these problems on the untyped api and modify the API to depend on the abstractions.
Comments: [Fixed](https://aspnetwebstack.codeplex.com/SourceControl/changeset/769e43f6f5f954987e763ac625b496ab4a4428ac).