* chore(ng2/dart): update from beta.1x to beta.18
Update made to all `pubspec.yaml` files and to relevant prose.
Note that pipes was back a beta.15; the rest were at beta.17.
* chore(pipes/dart): update ngFor microsyntax and transform method param
Updates to pipe example source code:
- Pipe `transform()` method parameters
- `ngFor` microsyntax, from `#` to `let`
