Added management for the grab-focus to a child widget, like a range, we need to fade...

Added management for the grab-focus to a child widget, like a range, we need to fade out the scrollbar when releasing.

* src/hildon-pannable-area.c,
	(hildon_pannable_area_init): Connected the grab-focus signal to
	the callback.
	(hildon_pannable_area_grab_notify): Added this function in order
	to manage the situation when the grab-focus ends. We have to
	fade-out the scrollbar.