We seemed to create more confusion by omitting app.module (and main) in QS than we gained in simplicity of QS
Every other example requires these files.
This PR restores them to QS _but doesn't talk about them_ in QS, leaving _that_ to the Setup guide.
* cache/quickstart sync before making Dart edits
* quickstart updates for Dart
* cache/guide/index sync before making Dart edits
* guide/index updates for Dart
* learning-angular for Dart
* guide/setup for Dart
* refresh cache/tutorial/index
