LPS-32847 Refactoring in the DDL/DDM export import

Hey Julio,

This is just a small refactoring what @KocsisDaniel made for the DDL/DDM export import.

The relationship between the entities was not handled properly.

You'll probably notice that some new methods have been added to the portlet data context regarding the element handling for the portlet-data.xml file, there is one more new method which basically extends that functionality.

Thanks,

Máté