feat(view): introduce free embedded views

Free embedded views are view instances that are created
logically in the same was as views of a ViewContainer,
but their dom nodes are not attached.

BREAKING CHANGE:

- `Renderer.detachFreeHostView` was renamed to
  `Renderer.detachFreeView`
- `DomRenderer.getHostElement()` was generalized into
  `DomRenderer.getRootNodes()`

modules/angular2_material/src/components/dialog/dialog.ts

@@ -66,7 +66,7 @@ export class MdDialog {
           // TODO(jelbourn): Don't use direct DOM access. Need abstraction to create an element
           // directly on the document body (also needed for web workers stuff).
           // Create a DOM node to serve as a physical host element for the dialog.
-          var dialogElement = this.domRenderer.getHostElement(containerRef.hostView.render);
+          var dialogElement = this.domRenderer.getRootNodes(containerRef.hostView.render)[0];
           DOM.appendChild(DOM.query('body'), dialogElement);
 
           // TODO(jelbourn): Use hostProperties binding to set these once #1539 is fixed.
@@ -111,7 +111,7 @@ export class MdDialog {
         .then((componentRef) => {
           // TODO(tbosch): clean this up when we have custom renderers
           // (https://github.com/angular/angular/issues/1807)
-          var backdropElement = this.domRenderer.getHostElement(componentRef.hostView.render);
+          var backdropElement = this.domRenderer.getRootNodes(componentRef.hostView.render)[0];
           DOM.addClass(backdropElement, 'md-backdrop');
           DOM.appendChild(DOM.query('body'), backdropElement);
           return componentRef;