New: Add initial bare-bones extension source code

I'm using version 1 for the first development phase (like what major
version zero (0.y.z) is in Semantic Versioning 2.0.0), so that the first
production version then gets version 2.

src/extension.js

@@ -0,0 +1,16 @@
+"use strict";
+
+class Extension {
+    constructor() {
+    }
+
+    enable() {
+    }
+
+    disable() {
+    }
+}
+
+function init() {
+    return new Extension();
+}

src/metadata.json

@@ -0,0 +1,7 @@
+{
+    "uuid": "top-bar-organizer@julian.gse.jsts.xyz",
+    "name": "Top Bar Organizer",
+    "description": "Organize the items of the top (menu)bar.",
+    "version": 1,
+    "shell-version": [ "40" ]
+}