POI markers slow to render after clicking a country

[reinierl]

When: I click the POI marker for The Netherlands on cycleplanet.org on my rather beefy development laptop

Then I expect: to see a map with markers rapidly

Instead: It takes about 7 seconds to load

It must be much worse on phones.

This turns out to be due to the client-side clustering. I have disabled that now and that speeds things up, although there is still a noticable delay when switching from marker counts to separate markers.