Remember last custom basemap

app/static/app/js/components/Map.jsx

@@ -384,12 +384,14 @@ class Map extends React.Component {
 
       const customLayer = L.layerGroup();
       customLayer.on("add", a => {
+        const defaultCustomBm = window.localStorage.getItem('lastCustomBasemap') || 'https://a.tile.openstreetmap.org/{z}/{x}/{y}.png';
+      
         let url = window.prompt([_('Enter a tile URL template. Valid coordinates are:'),
 _('{z}, {x}, {y} for Z/X/Y tile scheme'),
 _('{-y} for flipped TMS-style Y coordinates'),
 '',
 _('Example:'),
-'https://a.tile.openstreetmap.org/{z}/{x}/{y}.png'].join("\n"), 'https://a.tile.openstreetmap.org/{z}/{x}/{y}.png');
+'https://a.tile.openstreetmap.org/{z}/{x}/{y}.png'].join("\n"), defaultCustomBm);
         
         if (url){
           customLayer.clearLayers();
@@ -400,6 +402,7 @@ _('Example:'),
           });
           customLayer.addLayer(l);
           l.bringToBack();
+          window.localStorage.setItem('lastCustomBasemap', url);
         }
       });
       this.basemaps[_("Custom")] = customLayer;