Fixed placement of three.js examples

Three.js examples were placed in the root of Qt examples folder,
this moves them to be under canvas3d as they should be.

Change-Id: I506685d8a147975bc137fbac3b22d8ce28639631
Reviewed-by: Tomi Korpipää <tomi.korpipaa@theqtcompany.com>
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>