add clustering library

vendor/leaflet.markercluster/MarkerCluster.Default.css

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+.marker-cluster-small {
+	background-color: rgba(181, 226, 140, 0.6);
+	}
+.marker-cluster-small div {
+	background-color: rgba(110, 204, 57, 0.6);
+	}
+
+.marker-cluster-medium {
+	background-color: rgba(241, 211, 87, 0.6);
+	}
+.marker-cluster-medium div {
+	background-color: rgba(240, 194, 12, 0.6);
+	}
+
+.marker-cluster-large {
+	background-color: rgba(253, 156, 115, 0.6);
+	}
+.marker-cluster-large div {
+	background-color: rgba(241, 128, 23, 0.6);
+	}
+
+.marker-cluster {
+	background-clip: padding-box;
+	border-radius: 20px;
+	}
+.marker-cluster div {
+	width: 30px;
+	height: 30px;
+	margin-left: 5px;
+	margin-top: 5px;
+
+	text-align: center;
+	border-radius: 15px;
+	font: 12px "Helvetica Neue", Arial, Helvetica, sans-serif;
+	}
+.marker-cluster span {
+	line-height: 30px;
+	}

vendor/leaflet.markercluster/MarkerCluster.Default.ie.css

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+ /* IE 6-8 fallback colors */
+.marker-cluster-small {
+	background-color: rgb(181, 226, 140);
+	}
+.marker-cluster-small div {
+	background-color: rgb(110, 204, 57);
+	}
+
+.marker-cluster-medium {
+	background-color: rgb(241, 211, 87);
+	}
+.marker-cluster-medium div {
+	background-color: rgb(240, 194, 12);
+	}
+
+.marker-cluster-large {
+	background-color: rgb(253, 156, 115);
+	}
+.marker-cluster-large div {
+	background-color: rgb(241, 128, 23);
+}
+

vendor/leaflet.markercluster/MarkerCluster.css

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+.leaflet-cluster-anim .leaflet-marker-icon, .leaflet-cluster-anim .leaflet-marker-shadow {
+	-webkit-transition: -webkit-transform 0.25s ease-out, opacity 0.25s ease-in;
+	-moz-transition: -moz-transform 0.25s ease-out, opacity 0.25s ease-in;
+	-o-transition: -o-transform 0.25s ease-out, opacity 0.25s ease-in;
+	transition: transform 0.25s ease-out, opacity 0.25s ease-in;
+	}