map-click-handler.js: fast-forward current infobox animation to reset infobox opacity
map-click-handler.js: remove infobox when moved outside twice the viewport size
map-click-handler.js: use jquery.fadeOut instead of jquery.animate when appropriate
map-click-handler.js: fix/work around race condition not removing nearest circle

The circle might not got destroyed if the user was clicking in a very short
sequence on the map due to the delayed removal after fadeOut. This removes
all circles before adding a new one, working around that race condition.