Since AlignmentMorph is now obsolete what Morph should I use to make a 
horizontal collection of ButtonMorphs? I am building a SystemWindow with 2 
panes. The top pane is a PluggableListMorph for data selection and the 
bottom pane a row of ButtonMorphs for adding, editing and removing the 
items listed in the top pane.

Right now I am using RectangleMorph. Or should I just continue using 
AlignmentMorph?