QDockWidget: Public methods to add widgets or buttons to Titlebar

For a long time people have been requesting easier access to the buttons and other elements of the DockWidget Titlebar.

The solution for task 84543 was a big step to resolving this and Qt 4.3 introduced QDockWidget::setTitleBarWidget() which allows an arbitrary widget to be set as the title bar.

This is an all or nothing solution though, and requires the developer to reimplement the existing buttons and title when they may only want to perform a simple action such as add a new button or an icon.

It would be nice to have an easily subclassable QDockWidgetTitleBar widget with an exposed layout and functions to make creating custom titlebars simpler.