Wrong "Save" behaviour in non-circuit content views

[flandreas]

The "Save" behaviour of the non-circuit content views for truth tables and boolean expressions is wrong in the following aspects:

• Content is not cloned when opened. If you edit the contents and decide to close the view without saving, the edited content is still present in the current project/library.
• Missing "Do you want to save?" question when closing view that has modified data.