VOXELFORMAT: move region offset into SceneGraphTransform translation

[mgerhardy]

We should switch all regions in all volumes to start at 0,0,0 and put the previously used mins values of the region into the translation of the transform node.

• [x] qbcl
• [x] qb
• [x] qbt
• [ ] vox
• [ ] gox
• [ ] ....
• [x] ~~Remove voxel::Mesh::getOffset~~
• [ ] Translate/Shift actions in voxedit should not modify the mesh offset, but the node transform.
• [ ] Update the unittests to check for the transform - not for the regions after conversion.