Modified the overshooting effect to make it faster

Modified the overshooting effect to make it faster

* hildon/hildon-pannable-area.c,
(hildon_pannable_area_class_init): Increased the overshooting max
speed to get a faster effect.
(hildon_pannable_axis_scroll): Increased minimum speed and reduce
deceleration of the overshooting
(hildon_pannable_area_button_release_cb): Calculate initial
overshooting speed when finger on the screen using the distance to
launch the effect faster.

Fixes: NB#126115 (Pannable list overshooting is unusably slow for
lists with slow row renderers)