* docs(cache): misc adjustments for Dart
Dart cache adjustments:
- Add guide/index (it was being inherited directly from latest before).
- Add proper cache of `_quickstart_repo.jade` (it used to be just an
include).
Also:
- In `_quickstart_repo.jade` use variable set to URL of repo.
- Fix newly added link to Quickstart in guide/index.jade.
* dart/displaying-data: just use TS's _quickstart_repo