Ensure to show the scrollbars, if required, on the adjustment::changed signal

Ensure to show the scrollbars, if required, on the adjustment::changed signal
handler

* hildon/hildon-pannable-area.c
(hildon_pannable_area_initial_effect): Remove the initial_effect
management, check initial_hint
(hildon_pannable_are_expose_event): Remove the initial_hint management,
set initial_effect to FALSE
(hildon_pannable_are_refresh): Check if we need to show the scrollbars,
by launching the fade_timeout if the scrollbars state has changed and are
visible
* examples/hildon-pannable-area-initial-hint-example.c
Modified to allow to remove rows too. Add and remove rows one by one