Added a rudimentary primary key property to the meta-model and made it editable. Here's, what we have done so far:
- extend ActivityExtensions.ecore (maybe use an extra file in the future)
-- add the PrimaryKey type
-- add a relation for the primary key in the DocumentRoot
- generate the model code
- adjust the ItemAwareElementPropertiesBuilder
-- add a binding
--- this binding has to be handcrafted using the ExtensionUtil