Add and remove graphics from map.
Add and remove graphics from map.

Remember markers and paths so they can be removed from the map. That
way new markers and paths can be added without overburdening the map.

GENI-NSF/geni-demoviz,GENI-NSF/geni-demoviz,GENI-NSF/geni-demoviz,GENI-NSF/geni-demoviz