Restore window size/state issues

Application has closeEvent that saves geometry and state, ctor that restores them.

If the window is maximised when closed then the order of the code that restores the geometry appears critical.  If showMaximized() is called before setGeometry(screen()->availableGeometry()), then the window is shown with the title bar off screen at the top.  If the order is reversed the window is displayed as expected.   The correct order must be documented or if this shouldn't be critical the bug should be squashed.

Also if the window is maximised and restored while the application is running then the window size/geometry return to what they were before it was maximised, but if you maximise the window and close the application, and then reopen (to a maximised window), and then restore the window the size/geometry are not returned to the the prior condition, but to the smallest size the window and its dock widgets can be given its components.

For a discussion of this please see:

https://forum.qt.io/topic/151586/problem-with-maximised-window