Improve QML examples for Qt3D

Currently we have a lot of Qt3D C++ examples that effectively recommend some fairly advanced usage of Qt3D outside of the QML API. At the time of writing the following examples fit this:

• photobrowser3d
• pageflip
• nesting

We have already deprecated and removed the QGraphicsView related examples. With Qt5 the QML API becomes much more important, and very complex generic C++ examples only serve to make Qt3D less accessible, and do not illustrate Qt3D's primary API in a very good way. Encouraging the writing of Qt3D C++ code like for example photobrowser3d by continuing to support these examples into Qt5 will become unsustainable, and therefore they need to be replaced by equivalent QML examples that demonstrate how easy the same thing can be achieved in QML.