carto: add initMap method

app/javascript/shared/carto.js

@@ -6,6 +6,19 @@ import L from 'leaflet';
 export { DEFAULT_POSITION, LAT, LON };
 const LAYERS = {};
 
+export function initMap(position) {
+  const map = L.map('map', {
+    scrollWheelZoom: false
+  }).setView([position.lat, position.lon], position.zoom);
+
+  L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png', {
+    attribution:
+      '&copy; <a href="https://www.openstreetmap.org/copyright">OpenStreetMap</a> contributors'
+  }).addTo(map);
+
+  return map;
+}
+
 export function drawLayer(map, data, style, layerName = 'default') {
   removeLayer(map, layerName);