refactor(compiler): remove Viewport directives, use Decorator instead

BREAKING_CHANGE:
- The special type of `Viewport` directives is removed
  in favor of a more general `Decorator` directive
- `ViewContainerRef` now no more has a default `ProtoViewRef`
  but requires an explicit one when creating views.

Closes #1536

modules/angular2/test/router/outlet_spec.js

@@ -16,7 +16,7 @@ import {
 import {TestBed} from 'angular2/test';
 
 import {Injector, bind} from 'angular2/di';
-import {Component, Viewport} from 'angular2/src/core/annotations_impl/annotations';
+import {Component} from 'angular2/src/core/annotations_impl/annotations';
 import {View} from 'angular2/src/core/annotations_impl/view';
 
 import {RootRouter} from 'angular2/src/router/router';

modules/angular2/test/router/router_spec.js

@@ -9,7 +9,7 @@ import {
 import {IMPLEMENTS} from 'angular2/src/facade/lang';
 
 import {Promise, PromiseWrapper} from 'angular2/src/facade/async';
-import {RootRouter, Viewport} from 'angular2/src/router/router';
+import {RootRouter} from 'angular2/src/router/router';
 import {Pipeline} from 'angular2/src/router/pipeline';
 import {RouterOutlet} from 'angular2/src/router/router_outlet';