Create: Add a radio button to packages

Description of problem:
In the Data Modeler, when you click Create, it brings up a dialogue for creating a new data object. In this dialogue, you have to either choose an existing package for the new object or type in a new package to be created.
This choice is either / or, you can use both an existing package and a new one.
The GUI should reflect that - the choice should be done e.g. via radio buttons.
You shouldn't be allowed to specify both.