3D Floorplan 4.26.1

Fixed

• The 2D view no longer draws the hidden 3D picture (#542): with only the plan on the screen, the 3D view behind it was still drawn on every frame. Now it is drawn only when it can be seen: the 2D view is lighter for tablets and PCs (part of #138), and the plan answers at once where a slow 3D frame held its redraw back (the browser test part 48_plot failed now and then because of it; its check now also waits for the redraw). Back in the 3D or split view the picture is drawn at once.