Added rotation

The picture can now be rotated, scaled and pinned (still one finger
only)
Added panning with two fingers
A simple gallery app

The problem is that the onFling event doesn't fire.
Working fling
Added SimpleOnGestureListener

The main activity doesn't implement any interface. Instead I use the
overridden implementation of fling method in SimpleOnGestureListener.
The listener is set as a parameter at the constructor of the
gestureDetector. The code is cleaner and clearer this way.