Emscripten: added app manifest and favicon

os/emscripten/openttd.webapp

@@ -0,0 +1,13 @@
+{
+    "name":         "OpenTTD",
+    "short_name":   "OpenTTD",
+    "description":  "Open-source transport business simulation game",
+    "display":      "fullscreen",
+    "orientation":  "landscape",
+    "icons": [
+        {
+            "src": "openttd.256.png",
+            "sizes": "256x256"
+        }
+    ]
+}

os/emscripten/shell.html

@@ -4,6 +4,8 @@
     <meta charset="utf-8">
     <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
     <title>OpenTTD</title>
+    <link rel="manifest" href="openttd.webapp">
+    <link rel="icon" href="openttd.256.png">
     <style>
       body {
         font-family: Tahoma, Arial, Helvetica, sans-serif;