ScrollContainer: will auto-size better when not explicitly sized. added padding values (to allow background to be a border)
PickerList: docs tweaks
added Panel container (which could be used as a window) (closes #195)
added PanelScreen component
Layouts: helper vector is no longer static to avoid potential conflicts with nested layouts.
AnchorLayout: reorganized a bit
AnchorLayout: measurement without support for anchor display objects.
AnchorLayout: measurement accounts for anchor display objects