docs(guide/pipes): follow-up to #1654 (#1769)

Mainly Dart-side review, following #1654:
- Updates to follow style guide
- Suites passed:
  public/docs/_examples/pipes/dart
- Suites failed (known issue - #1761):
  public/docs/_examples/pipes/ts

public/docs/_examples/pipes/dart/lib/app_component.dart

@@ -16,11 +16,11 @@ import 'power_booster_component.dart';
       FlyingHeroesComponent,
       FlyingHeroesImpureComponent,
       HeroAsyncMessageComponent,
-      HeroBirthday,
-      HeroBirthday2,
+      HeroBirthdayComponent,
+      HeroBirthday2Component,
       HeroListComponent,
-      PowerBoostCalculator,
-      PowerBooster,
+      PowerBoostCalculatorComponent,
+      PowerBoosterComponent,
     ])
 class AppComponent {
   DateTime birthday = new DateTime(1988, 4, 15); // April 15, 1988

public/docs/_examples/pipes/dart/lib/hero_birthday1_component.dart

@@ -7,6 +7,6 @@ import 'package:angular2/angular2.dart';
     template: "<p>The hero's birthday is {{ birthday | date }}</p>"
     // #enddocregion hero-birthday-template
     )
-class HeroBirthday {
+class HeroBirthdayComponent {
   DateTime birthday = new DateTime(1988, 4, 15); // April 15, 1988
 }

public/docs/_examples/pipes/dart/lib/hero_birthday2_component.dart

@@ -11,7 +11,7 @@ import 'package:angular2/angular2.dart';
     // #enddocregion template
     )
 // #docregion class
-class HeroBirthday2 {
+class HeroBirthday2Component {
   DateTime birthday = new DateTime(1988, 4, 15); // April 15, 1988
 
   bool toggle = true;

public/docs/_examples/pipes/dart/lib/power_boost_calculator_component.dart

@@ -13,7 +13,7 @@ import 'exponential_strength_pipe.dart';
       </p>
     ''',
     pipes: const [ExponentialStrengthPipe])
-class PowerBoostCalculator {
+class PowerBoostCalculatorComponent {
   num power = 5;
   num factor = 1;
 }

public/docs/_examples/pipes/dart/lib/power_booster_component.dart

@@ -9,4 +9,4 @@ import 'exponential_strength_pipe.dart';
       <p>Super power boost: {{2 | exponentialStrength: 10}}</p>
     ''',
     pipes: const [ExponentialStrengthPipe])
-class PowerBooster {}
+class PowerBoosterComponent {}

public/docs/_examples/pipes/dart/web/main.dart

@@ -5,5 +5,5 @@ import 'package:pipe_examples/hero_birthday1_component.dart';
 
 main() {
   bootstrap(AppComponent);
-  bootstrap(HeroBirthday);
+  bootstrap(HeroBirthdayComponent);
 }