The application got unstable on exit under various conditions
(e.g. LayoutView created in script). Reason was the ownership
management of LayoutView which interfered with Qt widget
lifetime management.
The solution now is based on a clean widget/view hierarchy
and a consistent plugin parent/child relationship.
In addition, a new class is enabled which allows creating
a true QWidget (rather QFrame) for a LayoutView again.
Iterated instances are created for OASIS files
using irregular repetitions in viewer mode.
Reason: this way, the same drawing optimization
than for iterated shape arrays can be applied.
As this is a new API feature, some adjustments
had to be made to incorporate them into the
code.