Add support for Mac OS X's trackpad gestures

[CyberSkull]

For a few versions of Mac OS X now, iOS-like trackpad gestures have been available. These gestures would make Foldit easier to control.

There are several gestures that can be used:
Scrolling, tap to zoom, zoom in, zoom out, rotate.

Adding support for these gestures would really make Foldit much easier to control with a trackpad.