Add support for touch devices

[Lucki]

• When using a touch screen either with a finger or a pen the mouse is not at the desired pointed location. There's an offset to the actual location which changes when moving away from the screen and get back near to it.
• Automatically opening the on screen keyboard when focusing a text input field with a touch input would also be convienient.

I've tested this on Windows 10, other OSs may suffer with same problems.

[SimonN]

The root of all evil is the infinite mouse movement. The hardware cursor doesn't align with the Lix crosshair.

Thanks for testing! I accept that tablets are common, but this requires a large-scale revamping of internals. I'll defer this issue indefinitely, essentially it's wontfix, but maybe ask again over the years.