Remove redundant instance info from GUI

[zaucker]

The instance name occurs both in NavFolder and in PropTable (in each variable name). On rename, the latter was not updated and thus renaming of the instance immediately followed with a change in a input value, did

• not save the new input value for the renamed instance,
• but created a new instance (in the database only)

which only became obvious when reloading the dataset. This is currently fixed by updating the variable names in PropTable as well, but should be refactored by removing the instance name from the PropTable variable column.