WIP add pinch zoom

[m-novikov]

#!/usr/bin/env python3
from volumina.api import Viewer
from PyQt5.QtWidgets import QApplication

app = QApplication(["TestApp"])
app.setApplicationName("TestApp")
v = Viewer()
v.setWindowTitle("TestApp")
import numpy

a = numpy.random.randint(0, 255, size=(512, 512, 3), dtype=numpy.uint8)
v.addGrayscaleLayer(a, name="raw")
v.show()


def change():
    v.dataShape = (1, 100, 200, 300, 1)


# QTimer.singleShot(200, change)
app.exec_()

[m-novikov]

@emilmelnikov please test when you have the chance

[emilmelnikov]

Tried this on the latest Windows 10 (20H2) with the changes rebased on the current master, but pinch-to-zoom doesn't work.