Memleak fixes

* Set parent of title- and content-widget to associated container-widget
* inside FloatingWidget::takeContent(...)

Restore state
* Restore all contents as visible and then call hideSectionContent(...) at
* the end. This is more consistent and uses same code (public API).
* Pass version to sub-methods to handle different formats
* Fix serialization, if nothing is visible (no sections, only hidden
* contents)

AdvancedDockingSystem/src/SectionTitleWidget.cpp

@@ -31,6 +31,8 @@ SectionTitleWidget::SectionTitleWidget(SectionContent::RefPtr content, QWidget*
 	_tabMoving(false),
 	_activeTab(false)
 {
+	qDebug() << Q_FUNC_INFO;
+
 	QBoxLayout* l = new QBoxLayout(QBoxLayout::LeftToRight);
 	l->setContentsMargins(0, 0, 0, 0);
 	l->setSpacing(0);