The toolbar is a container, so can have other widgets added to it
as though it were a box container. Buttons should be added as
action items, so that they are rendered in the proper style. Check
buttons should be given the argument
addSpring to right align items.
passed to constructor
Helper to add a gaction item
Helper to add a separator
Map a toolbar list, a named list of gaction items or gsepartor items
Clear toolbar items
What widget do we use for the parent of the children
We can't really adjust spacing between children after they have been positioned.