[FEATURE] Added enchanced weighted smoothing algorithm with tail configuration

Now when you lift up the stylus the line hurries to the tip of the pen
so that the line ends right at the position of the pen, not delayed.

There is a configuration option for this feature: "Tail Aggressiveness"
(probably, some other name would be better ;) )

1) Tail Aggressiveness == 0:    There is no tail at all. The line ends where it was.
2) Tail Aggressiveness == 0.15: The tail ends with the very thin tip.
3) Tail Aggressiveness >  0.15: The tail ends with bolder tip.

CCMAIL:kimageshop@kde.org