chore(test): migrate Dart tests to package:test

Instead of running with karma and the karma-dart shim, run dart
tests directly using the new package:test runner. This migrates
away from package:unittest.

Fixes a couple tests, mostly associated with depending on absolute
URLs or editing the test providers after an injector had already
been created.

Remove karma-dart and associated files. Change gupfiles to run tests
via `pub run test` instead.

modules/angular2/pubspec.yaml

@@ -23,6 +23,7 @@ dependencies:
 dev_dependencies:
   transformer_test: '^0.2.0'
   guinness: '^0.1.18'
+  guinness2: '0.0.5'
   quiver: '^0.21.4'
   test: '^0.12.6'
 transformers: