Option to turn keystone loupe on and off

Please add an option to toggle the keystone loupe on and off, for instance by using a modifier key when holding and dragging the adjustment points.

While it's nice to finally have the loupe, it's something of a disadvantage not being able to turn it off as it blocks the view of the guides.

As the adjustment points are locked together, it's often difficult to place them correctly without using the guides (by making either horizontal or vertical adjustments first, then placing the corresponding guides and using them to align the adjustment points for full horizontal and vertical adjustments). This workaround has been made more difficult now.

The problem isn't only with the guides though. The loupe is useful when you can see exactly where an adjustment point is to be placed, but in many cases this isn't the case, for instance if you have a rectangular figure with slightly rounded corners, or something else is covering a corner. In these cases you need to see the area surrounding the corner, which the loupe is now blocking. For this reason, making it possible to either hide or show the loupe by pressing a modifier key while dragging the adjustment points would be the best solution. While the first problem (the loupe blocking the guides) could be solved by displaying the guides in the loupe, this wouldn't solve the second problem (with rounded corners etc.).