Fixed texture loading for json examples.

The models were too optimized. Since each face converging at one vertex
could have different texture coordinates, we need to make vertices
of each face unique, so that we can have unique texture coordinates
for each of them. Naturally this increases the rendered vertex count
significantly, but at least the textures are now mapped correctly.

Change-Id: I72b4705de5dd11263898eaf6c88f66a7dc232e1d
Task-number: QTBUG-42641
Reviewed-by: Tomi Korpipää <tomi.korpipaa@theqtcompany.com>
Reviewed-by: Pasi Keränen <pasi.keranen@digia.com>