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`).

modules/di/pubspec.yaml

@@ -5,4 +5,5 @@ dependencies:
   facade:
     path: ../facade
 dev_dependencies:
-  unittest: '>=0.10.1 <0.12.0'
+  test_lib:
+    path: ../test_lib

modules/di/src/key.js

@@ -0,0 +1,3 @@
+export class Key {
+
+}

modules/di/src/module.js

@@ -1,5 +1,6 @@
 import {Type} from 'facade/lang';
 import {Map, MapWrapper wraps Map} from 'facade/collection';
+import {Key} from './key';
 
 /// becouse we need to know when toValue was not set.
 /// (it could be that toValue is set to null or undefined in js)