Thank you Emmanuel for you feedback
I didn't know macOS' mice lack the middle button. I apologize for this, I'll try to implement an alternative method of enabling panning (I'm thinking of holding a key such as ALT while dragging).Adding a limit for the backward movement shouldn't be a problem. Moreover I also didn't implement the speed switch with the SHIFT key, but I can add it too.
Please note that I've substantially changed the way the scroll wheel moves the camera from linear to an exponential fashon, this way it acts much as a "zoom" than as navigation, which I find more confortable. However I understand some users could like the default behaviour, so I'm thinking about introducing a dialog to customize these settings.
Best regards,
Daniele