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/dom/html_adapter.dart

@@ -317,10 +317,10 @@ class Html5LibDomAdapter implements DomAdapter {
     throw 'not implemented';
   }
   bool supportsDOMEvents() {
-    throw 'not implemented';
+    return false;
   }
   bool supportsNativeShadowDOM() {
-    throw 'not implemented';
+    return false;
   }
   getHistory() {
     throw 'not implemented';