Update 'Debugging Qt Quick Projects' section

Setting Up QML Debugging

'DEFINES += QMLJSDEBUGGER.' isn't needed any more. Instead people will have to link in the static qmljsdebugging library under Project -> Build Settings -> qmake Step.
Whether the Qt configuration is debug or release doesn't matter any more.

Inspecting QML at Runtime

• The QmlObserver tab now shows the properties of the currently selected object
• the toolbar has moved out of the tab in the toolbar menu.
• The Toolbar is now also available at runtime in a separate window.

Security considerations

We should add a section about the security implications when debugging helpers are linked in.