refactor: simplify and make tests work in JS and Dart

* remove `wraps` syntax enhancements for imports
  and support new `import * as module from ...` syntax

  - default imports are the wrong construct for importing
    everything from a module

* moved tests from transpiler to jasmine and karma

  - transpiler tests are included when running karma in main project folder
  - transpiler is reloaded after every test run in karma,
    so no need to restart karma when the transpiler has been changed.
  - removed own gulp build for transpiler and `postinstall.sh`
    as they are no more needed.
  - transpiler tests are now executed in Dart AND JavaScript (used to be executed
    only in Dart), which allowed to catch some bugs (see the bug with the
    import specification above).

* made tests work in dart as well by using the following hack:

  - dependencies are loaded from the `build` folder, which makes
    running `gulp build` necessary before running karma for dart
  - for this to work,
    the dependencies are included in main `pubspec.yaml` of project
  - reason for the hack: `karma-dart` loads all `packages` urls
    directly from disc (should rather use the karma file list)

* added explicit annotations `FIELD`, `ABSTRACT`, ... to `facade/lang.*`

  - needed for now that we can run tests and don't get errors for undefined
    annotations.

* added `README.md` with details about the build and tests

tools/transpiler/spec/functions_spec.js

@@ -1,7 +1,13 @@
+import {describe, it, expect} from 'test_lib/test_lib';
+
 function sum(a, b) {
   return a + b;
 }
 
-function main() {
-  assert(sum(1, 2) == 3);
+export function main() {
+  describe('functions', function() {
+    it('should work', function() {
+      expect(sum(1, 2)).toBe(3);
+    });
+  });
 }