gets called to notify a controller that a toolbar function has been selected.
Parameter aToolbarRes
a string which identifies the toolbar where the function has been selected.
Parameter aCommand
a string which identifies the function that has been selected.
This notification is normally used to implement the toolbar button/sub-toolbar
function feature. It exchanges the function of the toolbar button, that opened
the sub-toolbar, with the one that has been selected on the sub-toolbar.