Classes should be generated for typedef and grouping of same name

When using sal code generator with yang maven plugin on a yang file with typedef and grouping sharing the same name, no warning is produced and only the code for typedef is generated.

example yang file content:

typedef network-topology-ref

{ type instance-identifier; ... }

grouping network-topology-ref {
leaf network-topology-ref

{ type network-topology-ref; mandatory true; ... }

}

This should result in generating one class representing typedef network-topology-ref and one interface representing grouping.

This will require new binding specification.