Selectively highlight or expose stories with a given label

Toggle label highlighting on and off from the Labels & Saved Searches pane, so that you can make labeled stories easier to see in the backlog. For instance, click "needs design" once and all stories with that label in the backlog are highlighted, showing visually how much of the next few iterations are gated by designer availability.

This idea came from the wonderful users at our first SF Tracker Users Group.