Add mouse scroll wheel support for zooming.

1) Untested so far
2) OnGenericMotionListener is API 12, so cannot be used as is, but requires
wrapping in proxy classes to be upstream-ready.
Do adaptive mouse wheel processing to provide good zoom speed and precision.

As comments say, despite Google APU docs say that AXIS_VSCROLL should be
in range [-1.0; 1.0], real device may have quite different ranges.