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/MainWindow.cpp

@@ -1193,6 +1193,10 @@ void MainWindow::closeEvent (QCloseEvent * e)
             (*it)->hide();
             (*it)->deleteLater();
         }
+
+        if (Workbench* wb = WorkbenchManager::instance()->active())
+            wb->removeTaskWatcher();
+
         d->activityTimer->stop();
         saveWindowSettings();
         delete d->assistant;