implement show/hide layer with scripting

maps/tests/iframe_api.json

@@ -1,4 +1,11 @@
 { "compressionlevel":-1,
+ "editorsettings":
+    {
+     "export":
+        {
+         "target":"."
+        }
+    },
  "height":10,
  "infinite":false,
  "layers":[
@@ -49,6 +56,18 @@
          "x":0,
          "y":0
         }, 
+        {
+         "data":[0, 0, 93, 0, 104, 0, 0, 0, 0, 0, 0, 0, 104, 0, 115, 0, 0, 0, 93, 0, 0, 0, 115, 0, 0, 0, 93, 0, 104, 0, 0, 0, 0, 0, 0, 0, 104, 0, 115, 93, 0, 0, 0, 0, 0, 0, 115, 0, 0, 104, 0, 0, 0, 0, 0, 0, 0, 0, 0, 115, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
+         "height":10,
+         "id":6,
+         "name":"Metadata",
+         "opacity":1,
+         "type":"tilelayer",
+         "visible":true,
+         "width":10,
+         "x":0,
+         "y":0
+        }, 
         {
          "draworder":"topdown",
          "id":3,
@@ -78,11 +97,11 @@
          "x":0,
          "y":0
         }],
- "nextlayerid":6,
+ "nextlayerid":7,
  "nextobjectid":3,
  "orientation":"orthogonal",
  "renderorder":"right-down",
- "tiledversion":"2021.03.23",
+ "tiledversion":"1.4.3",
  "tileheight":32,
  "tilesets":[
         {
@@ -100,6 +119,6 @@
         }],
  "tilewidth":32,
  "type":"map",
- "version":1.5,
+ "version":1.4,
  "width":10
 }