refactor(change detect): Clean up change detector test layout

- Rename simple_watch_config > change_detector_config
- Add a bunch of comments explaining what's going on with the change
  detector tests.

Closes #2468

modules/angular2/test/change_detection/generated/change_detector_classes.ts

@@ -1,4 +1,5 @@
 // Ignore me, needed to support Angular 2 Dart.
+// See ../change_detector_spec for more details.
 
 export function getFactoryById(id: string) {
   return null;