I wanted a toolbar icon to run "Clean with last settings" without having to go to navigate down the plugins menu, so I added the following code to core.rb under the ### MENU & TOOLBARS ### section:

toolbar = UI;;Toolbar.new(PLUGIN_NAME)
cmd = UI;;Command.new("Cleanup"){ Sketchup.active_model.select_tool(self.cleanup_last) }
cmd.small_icon = "broom-24.png"
cmd.large_icon = "broom-48.png"
cmd.tooltip = "Cleanup"
cmd.status_bar_text = "Clean your model using current settings"
cmd.menu_text = "Cleanup"
toolbar = toolbar.add_item(cmd)
if toolbar.get_last_state==TB_NEVER_SHOWN
  toolbar.show
elsif toolbar.get_last_state==TB_VISIBLE
  toolbar.restore
end

I have attached the icons I used. They need to be placed in the same folder as core.rb