Improve restoration of windows geometry on launch

[philipstarkey]

We currently try and restore the window geometry on launch, but this doesn't always work correctly and the window ends up hidden off screen. The solutions to this are then to:

• Delete the _BLACS.h5 file in the labconfig folder, or
• Use the operating system controls to move the window (e.g. on Windows, right click on the window preview, click move, hit a keyboard arrow key, and then move the mouse).

We can probably restore the geometry in a way that doesn't trigger this issue, perhaps using QWidget.restoreGeometry() (see https://doc.qt.io/qt-5/restoring-geometry.html). However, I have a feeling I've tried this in the past and the downside was that it lost the window position when saving geometry of a maximised window. But maybe those issues have been resolved in Qt5 so we should investigate!