WIP: 3783

The branch 3783 contains new features:

• Set an Argument Element as Impacted
• Property section for changes that are made
• Propagate an impact of an argument elements to the other nodes of the diagram
• The user can change the state of the GSN node from the check-boxes in the property section (set as private/instantiated/undeveloped entity)
• The user can make a reference to a System Model Element and then select the element from the reference list he wants to go to

An error appears when saving the model: