MIRA: "relations between requirements"
1. At the moment requirements can be added to the relations table by drag and dro But they can not be deleted or removed. Then always the whole relation has to be deleted. They should be deleted when pressing on the delete button and alternatively when dragging them back to the model navigator.
2. Undirected requirements still have the arrows to include requirements to the tracing. The dialog should work the same and look the same as the dialog of directed requirements.
3. Please have a look on the exceptions occuring when modifying the relations.
(from redmine: issue id 1982, created on 2014-03-13, closed on 2014-06-16)