bpmn icons label missing (#435)

Dear,

Several icons like "event" and "gateway" accept a text field.

they resize as if the text is in there, but no text is shown.

instead these icons shoudn't contain text (as they can contain an image) and they shoudn't resize.

they should have a "label" linked to them as is the case with the "flow arrows"

http://camunda.org/bpmn/examples/ can give you some indicaton on what icons better use a "label" instead of "text inside the icon"