Don't allow panning while animation is playing

[heese]

The slider gets confused if an animation is playing (e.g., if you use a timeout to move to the next slide automatically) and the user pans the current slide. Usually, it ends up with two slides showing at the same time. I have introduced another flag indicating whether the user is panning around the current slide. The code does not allow for panning while an animation is playing and vice versa. There is also a new flag allowing for disabling manual slide changes.

I still can't run the demo and, therefore, cannot test the code in its native environment :-( Please, have a go -- any bugs should be easy to fix.