refactor(shadow_dom): remove ShadowDomStrategy in favor of @View(encapsulation)

BREAKING CHANGES:
- `ShadowDomStrategy` was removed. To specify the encapsulation of a component use `@View(encapsulation: ViewEncapsulation.NONE | ViewEncapsulation.EMULATED | ViewEncapsulation.NATIVE)`
- The default encapsulation strategy is now `ViewEncapsulation.EMULATED` if a component contains styles and `ViewEncapsulation.NONE` if it does not. Before this was always `NONE`.
- `ViewLoader` now returns the template as a string and the styles as a separate array

modules/angular2/src/facade/collection.dart

@@ -212,4 +212,7 @@ void iterateListLike(iter, fn(item)) {
 class SetWrapper {
   static Set createFromList(List l) => new Set.from(l);
   static bool has(Set s, key) => s.contains(key);
+  static void delete(Set m, k) {
+    m.remove(k);
+  }
 }

modules/angular2/src/facade/collection.ts

@@ -290,4 +290,5 @@ var createSetFromList: {(lst: List<any>): Set<any>} = (function() {
 export class SetWrapper {
   static createFromList<T>(lst: List<T>): Set<T> { return createSetFromList(lst); }
   static has<T>(s: Set<T>, key: T): boolean { return s.has(key); }
+  static delete<K>(m: Set<K>, k: K) { m.delete(k); }
 }