Made it possible to change the layout options in any animation mode

This fixes #1.
Made it possible to change the layout options in any animation mode.
The animation thread is now interruptible and stopAnimation will interrupt it.
The only thing I don't like so much is that it will disable the options after each slider step.
So you have to wait until the animation finished to change the slider setting (node size etc.) further.
But it's a minor usability thing, not so important.