App/Gui: fix memory leaks:

+ add function to cleanup units and quantities in debug build
+ fix reference leak in PropertyVector::getPyPathValue()
+ fix reference leak in PropertyPlacement::getPyPathValue()
+ in InterpreterSingleton::init() use a static std::vector<wchar_t*> instead of a C array
  to free memory at program end
+ in MainWindow::closeEvent() explicitly delete all task watchers
+ in ReportOutputObserver constructor pass parent to QObject
+ in PropertyEditor destructor explicitly delete QItemEditorFactory

src/Gui/propertyeditor/PropertyEditor.cpp

@@ -83,6 +83,9 @@ PropertyEditor::PropertyEditor(QWidget *parent)
 
 PropertyEditor::~PropertyEditor()
 {
+    QItemEditorFactory* f = delegate->itemEditorFactory();
+    delegate->setItemEditorFactory(nullptr);
+    delete f;
 }
 
 void PropertyEditor::setAutomaticExpand(bool v)