Toggle between "show at 100%" and "fit into window" by middle mouse button
I often use the mouse wheel for zooming. But it is difficult to zoom exactly to 100% by the mouse wheel. Therefore, if the option "Mouse Wheel Zooms" is activated, then please offer the following additional feature: Any click with the middle mouse button toggles between "Show the image at 100%" and "Fit image into window". In detail: If the image actual fits into the window, then a middle mouse click zooms it to 100% with the position clicked on being centered; if the image actual is shown magnified or shrinked, then a middle mouse click fits it into the window.