WIP: Add Pinch and Rotate gesture interactions to 3D view
Will not be functional until VTK forwards gesture events from QVTKOpenGLWidget using QVTKInteractorAdapter.cxx. (see merge request vtk/vtk!4398 (merged))
Example video: https://www.dropbox.com/s/6k76e17d2hvcdgy/gesture_interaction.mp4?dl=0
Cc: @lassoan