Remplace GLTF only when we save a improvement

[gdozot2]

When we validate an image, we can improve the submitted result. In case of a position computation is requested, we overwrite the old GLTF and replace it by the new one. The problem is in case of we cancel the improvement. The GLTF is not reverted and is as possibly an bad position.

We should create and temp area to manage this case and replace the official only when we save the improvement

[gdozot2]

After a second check, the main problem is not in case of cancel. But if we close the page without the cancel or if the computation during the cancel has a problem.