Backend refactoring

Minimized references to frontend elements from the backend.
QNode now has a uuid.
simple-qml update to use an instanciator.
Changed slightly the way LoadDataMeshJobs works.

Change-Id: If2866eb124bf9c026098ea0c70ae197101e9553e
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>
QEntity : Reordered component notifications

Change-Id: Ibdeef1a69573f22e76618fa0c2ffb15884d0180a
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>