[RFC190/212] Reference can specify both method and field

With the latest changes of the DS spec, a reference can specify both, a field and bind/unbind methods. Right now the implementation uses one or the other. We have to find a way to support both at the same time.
djencks Do you have an idea on how to fix this? One way would be to internally handle this as two references, but maybe there is a better way.

PS: The DTOs will be updated to reflect this; we have to wait until this change is done