Add suggestion for action icon

PROBLEM
In designer when creating an action, you need to know the name of the icon to use in the corresponding field as no suggestion is provided.

TODO

• Provide a suggestion for icon when people choose the designer option to create a "simple" action that uses the nuxeo-operation-button.
• Behavior should be similar to the other designer areas, e.g. when creating a search left menu item.

ACCEPTANCE CRITERIA

• When I create a "simple" action, a suggestion is offered for the icon field showing the icon and icon name
• When I select an icon, the name is persisted in the field
• When I create an advanced action, no suggestion is offered in the icon field (NOTE: check with web ui dev team for this one for what makes sense)