If you, like me, missed the news be aware that Oracle SQL Developer Data Modeler is now Free! (I think you already knew that from the title of this post :-))
Download and use it!
I, finally, will leave Oracle Designer to die...
Oracle SQL Developer Data Modeler provides modeling for Entity Relationship Diagrams (ERD), Relational (database design), Data Type and Multi-dimensional modeling, with forward and reverse engineering and DDL code generation.
The Data Modeler imports from and exports to a variety of sources, including XML.
And so, finally, I will get my DB model inside my source control system!