ration dots above certain levels to keep Leaflet happy

[burritojustice]

Displaying a large number of dots can cause Leaflet to stop updating, giving the appearance that the search tool has crashed, even though it is happily geocoding underneath the covers.

The appearance of dots are very exciting! So we should keep that as dynamic as possible, at least at the start.

A possible solution: above some threshold (say 500 results), display every 10th dot, and above 1000 only display every 20th or 100th dot or something reasonable.