Changes
#* '''TARGETTYPELEFT''': reference to the MetaClass of the right object of the relation
#* '''TARGETTYPERIGHT''': reference to the MetaClass of the left object of the relation
#* '''RELATIONDATA''': reference to the MetaClass used as template for the relational data#: <p>either by</p>
#* dragging and dropping a MetaClass object onto the cell
#* selecting the desired MetaClass from the dialog appearing after double-clicking the cell
