Support multi-touch pinch zoom and rotate gestures on windows precision touchpad (PTP)

This is the (not so) new touchpad standard that windows 10 is pushing, and I would expect more laptop manufacturers to support this.

Qt seems to already handle the gesture on Macbooks (OS X), as seen from D8121.

We can probably enable it easily if Qt decides to add support for it. Otherwise we might be able to implement it in Krita with our own code... and possibly submit a patch upstream after that?...

Or should I just create a wish on the Qt bugtracker...

(The problem is, I haven't even managed to find the corresponding APIs...)

For reference: Synaptics and Wacom (and possibly other) have their own multi-touch API for their touchpads, but I don't suggest supporting those since they aren't endorsed by the OS, can break at any time (read: breaks more easily than windows built-in functions), and can become a huge mess.