Make render() call explicit
Construct RenderImage from bounds, not Shape*
Disable 2D rendering for the moment
Store position in depth image.

(doesn't yet work because of scale factor, but incremental progress)
Make render image scale explicit
Fix depth image positioning
Clarify comments
DepthImages are now drawn with appropriate scale.

(depth scaling still doesn't work)
Improving depth image scaling (still not totally working)
Depth image scaling now works.
Force at least one voxel in Z direction
Helper function turns QMatrix4x4 into Transform
Clarifying comments
Enable 2D rendering (with strange crashes)
Use deleteLater (since DepthImageItem is now a QObject)
Fix silly trick to make 2D shapes render properly
Resolution refinement now works
Merge branch 'render-refinement'