These are for tweaking the popup position according to the current
style. First usage goes to ComboBox.

Also prepares for proper support of 'small' and 'mini' style hints.

Change-Id: I7bc682d5d82bf6fa7a36916a9d4c64dfb2bdb56e
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>