Enable smooth scrolling and zooming on platforms that supports this

On platforms that support smooth (high-resolution) scrolling, zooming in LibreCAD is almost impossible. For each pixel the cursor moves, the view is zoomed 25 %. This patch enables native zoom events (pinch zoom) on supported platforms as well as swapping pan and zoom functionality for input devices supplying high resolution 2D scrolling inputs.

Note: Has only been tested on Mac with a multi-touch trackpad where it makes the scrolling and zooming paradigm match the OS conventions.