add zoom function when scrolling the mousewheel while left shift is pressed
pressing SPACE causes zoom-factor to smoothly go to default position (like the rotation)
Merge branch 'enable_zooming' into hand_of_god
add default transform matrix to Hand which does the scaling and rotation to default position
add first linking between mouse position (screen) and Hand position (world).

for now, simple mapping of screen X,Y coordinates to world X,-Z coordinates.