Add support in Designer for foreign keys cross models

Add support in Designer for foreign keys cross models.

In Designer you cannot have a FK cross models. That is not a limitation with DDL metadata in Teiid. It's a misstatement to relate that to optimization. If the PK/FK is present we'll use that information just as we would in a single source - we do not however enforce the FK. That can be done through the use of an update procedure though.