Add leaflet clustering with leaflet.markercluster.

First preliminary version with clustered berries.
Make marker removal clustering compatible.
Explicit plant rotation.
Performance improvements for clustering.
Better icon anchor.
Correct colors for search result list clusters.
Clustermarker stylesheet
Decrease cluster size.
Handle all colors of service cart.
Handle units without geometries on map refit.
Handle removing services in a cluster compatible way.
Don't draw units for already cancelled services.

Fixes #76. Test and think whether we should
also cancel the fetch requests.
Fix style.
Simplify pagination.
Simple circle drawing for markers.
Reorganize widget hierarchy.
Point based clustering.
Fix filename for marker cluster css.
Tweak markers.