#122 discovered an icon menu behavior:
Enable/Disable - enable/disable an icon menu for the element. make an icon block invisible
Show/Hide - on mouse enter/exit from the diagram element
extendMenus - extend an existing menus list
load - create an icon bar if corresponding menu exists

There is an idea to create a common menus for all diagram with the same type. Therefore we need to enable/disable icon menu on focus change.