chore: karma with JS, Dart

Note: karma with dart is still not working
because of how `karma-dart` loads `package:…` dependencies.

Usage:
```
karma start karma-js.conf.js
karma start karma-dart.conf.js
```

Make sure to set `DARTIUM_BIN` env variable.

Refactors `js2dart`:
- live outside of the traceur module (`tools/js2dart/index.js`)
  so it can be reused by gulp and karma
- automatically build the sources in memory,
  so that `js2dart` can be used without running `gulp build` first
- provide a way to specify the moduleName of a compilation run
  independently of the input filename. This helps error messages
  and source maps (not yet enabled) to report the correct file name

Changes project setup:
- add module `test_lib` that contains the primitives for tests
  (e.g. `describe`, `it`, …)
- clean up some sources that had errors in them
- module names in transpiled js and dart files don’t contain
  `lib`, `test` nor `src` any more (e.g. `di/di`).

karma-dart.conf.js

@@ -0,0 +1,61 @@
+// Karma configuration
+// Generated on Thu Sep 25 2014 11:52:02 GMT-0700 (PDT)
+
+module.exports = function(config) {
+  config.set({
+
+    frameworks: ['dart-unittest'],
+
+    files: [
+      {pattern: 'packages/**/*.dart', included: false},
+      {pattern: 'modules/*/src/**/*.js', included: false},
+      {pattern: 'modules/*/test/**/*.js', included: true},
+      {pattern: 'modules/**/*.dart', included: false},
+      'packages/browser/dart.js'
+    ],
+
+    karmaDartImports: {
+      guinness: 'package:guinness/guinness_html.dart'
+    },
+
+    preprocessors: {
+      'modules/**/*.js': ['traceur']
+    },
+    customFileHandlers: [{
+      urlRegex: /.*\/packages\/.*$/,
+      handler: function(request, response, fa, fb, basePath) {
+        var url = request.url;
+        var path = url.indexOf('?') > -1 ? url.substring(0, url.indexOf('?')) : url;
+        var contets = fs.readFileSync(basePath + path);
+        response.writeHead(200);
+        response.end(contets);
+      }
+    }],
+    traceurPreprocessor: {
+      options: {
+        outputLanguage: 'dart',
+        script: false,
+        modules: 'register',
+        types: true,
+        // typeAssertions: true,
+        // typeAssertionModule: 'assert',
+        annotations: true
+      },
+      resolveModuleName: function(fileName) {
+        var moduleName = fileName
+          .replace(/.*\/modules\//, '')
+          .replace(/\/src\//, '/')
+          .replace(/\/test\//, '/');
+        return moduleName;
+      },
+      transformPath: function(fileName) {
+        return fileName.replace('.js', '.dart');
+      }
+    },
+
+    browsers: ['Dartium']
+  });
+
+
+  config.plugins.push(require('./tools/js2dart/karma-traceur-preprocessor'));
+};