Allow layer command of none to remove base layer

README.md

@@ -323,6 +323,10 @@ style server by adding a property `wms: true`. (see overlay example below)
         "opt":{ "maxZoom":19, "attribution":"© OpenStreetMap" }
     };
 
+Note: you can use the name "none" to completely remove the base layer for example.
+
+   msg.payload = {"command":{"layer":"none"}};
+
 #### To add a WMS overlay layer - eg US weather radar
 
 To add an overlay instead of a base layer - specify the `overlay` property instead of the `name`.

worldmap/index.html

@@ -1756,6 +1756,10 @@ function doCommand(cmd) {
         baselayername = cmd.layer;
         basemaps[baselayername].addTo(map);
     }
+    if (cmd.layer && (cmd.layer === "none")) {
+        map.removeLayer(basemaps[baselayername]);
+        baselayername = cmd.layer;
+    }
     // Add search command
     if (cmd.hasOwnProperty("search") && (typeof cmd.search === "string")) {
         document.getElementById('search').value = cmd.search;

worldmap/worldmap.appcache

@@ -1,5 +1,5 @@
 CACHE MANIFEST
-# date: Mar 2nd 2019 - v1.5.29c
+# date: Mar 2nd 2019 - v1.5.29d
 
 CACHE:
 index.html