Refactor examples and demos

The Qt3D examples and demos are crufty and in some cases buggy. Work needing to be done includes:

1. Remove examples or parts of examples that do not relate to our current work and focus - for example relating to graphicsview or stereo
2. Examples should demonstrate our API's clearly - if an example is about something we do not currently recommend or support it should be removed or refactored
3. Check that the documentation here: http://doc.qt.nokia.com/qt-quick3d-snapshot/qt3d-examples.html actually matches the example, is correct and up-to-date

Make sure that examples run on the supported platforms - for Qt internals see this bug: http://nok/1mw