Add some structure for interactive tests of UI components

js/ui/environment.js: Split out initial UI setup (Tweener initialization,
  Nbtk monkey-patching) into a separate file we can import from tests.

tests/: Directory for various types of tests
tests/run-test.sh: Shell script that to run tests with an appropriate
  environment set up.

tests/testcommon/: Common modules and data for tests
tests/interactive/: Interactive tests

tests/interactive/box-layout.js: A sample test of NbtkLayout

tests/interactive/box-layout.js

@@ -0,0 +1,39 @@
+/* -*- mode: js2; js2-basic-offset: 4; indent-tabs-mode: nil -*- */
+
+const Clutter = imports.gi.Clutter;
+const Nbtk = imports.gi.Nbtk;
+
+const UI = imports.testcommon.ui;
+
+UI.init();
+let stage = Clutter.Stage.get_default();
+
+let b = new Nbtk.BoxLayout({ vertical: true,
+			     width: stage.width,
+			     height: stage.height });
+stage.add_actor(b);
+
+let b2 = new Nbtk.BoxLayout();
+b.add(b2, { expand: true, fill: true });
+
+let r1 = new Nbtk.BoxLayout({ style_class: 'red',
+                              width: 10,
+                              height: 10 });
+b2.add(r1, { expand: true });
+
+let r2 = new Nbtk.BoxLayout({ style_class: 'green',
+                              width: 10,
+                              height: 10 });
+b2.add(r2, { expand: true,
+             x_fill: false,
+             x_align: Nbtk.Align.MIDDLE,
+             y_fill: false,
+             y_align: Nbtk.Align.MIDDLE });
+
+let r3 = new Nbtk.BoxLayout({ style_class: 'blue',
+                              width: 10,
+                              height: 10 });
+b.add(r3);
+
+stage.show();
+Clutter.main();