broadcast popup labels and event data now have the trigger name if there is no real data to show

fixes #1631 

STR: new app, add media player, a button hooked up to media-listen:play, a counter hooked up to media-broadcast:playing

when you hit the button, right now the broadcast and listen bubbles show "undefined". With the patch, they will both say "playing"
So, down the road, let's pull this from /component/broadcast/ because this won't exist as an attribute.