Use G_PRIORITY_IDLE_HIGH + 20 for all the pannable area timeouts

Use G_PRIORITY_IDLE_HIGH + 20 for all the pannable area timeouts

* hildon/hildon-pannable-area.c:
(hildon_pannable_area_launch_fade_timeout),
(hildon_pannable_area_motion_event_scroll),
(hildon_pannable_area_check_move),
(hildon_pannable_area_button_release_cb),
(hildon_pannable_area_scroll_to):

Use a priority of G_PRIORITY_IDLE_HIGH + 20 for all the pannable
area drawing operations, since this is the recommended for drawing
operations.

Fixes: NB#110894 (In event view containing very large description
field, application menu is displayed blank while panning)
Fixes: NB#131942 (HildonPickerDialog is seen empty when popping up
for the first time)