refactor(render): remove recursion from renderer

The goal is to make implementing a renderer straight forward.

BREAKING_CHANGE:

- Renderer interface was redone / simplified.
- `DirectDomRenderer` was replaced by `DomRenderer`.
- `DirectDomRenderer.setImperativeComponentRootNodes` is replaced
  by the following 2 steps:
    1. `ViewManager.getComponentView(elementRef) -> ViewRef`
    2. `DomRenderer.setComponentViewRootNodes(viewRef, rootNodes)`
- all `@View` annotations need to have a template, but the template
  may be empty. Previously views that had a `renderer` property did
  not have to have a `template`.
- `dynamicComponentLoader.loadIntoNewLocation` does no more allow
  to pass an element, but requires a css selector.
  Special syntax: `:document` can be used as prefix to search globally
  on the document instead of in the provided parent view.

Part of #1675

modules/angular2_material/src/components/dialog/dialog.js

@@ -22,6 +22,7 @@ import {View} from 'angular2/src/core/annotations_impl/view';
 // TODO(jelbourn): Pre-built `alert` and `confirm` dialogs.
 // TODO(jelbourn): Animate dialog out of / into opening element.
 
+var _nextDialogId = 0;
 
 /**
  * Service for opening modal dialogs.
@@ -49,7 +50,7 @@ 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 = DOM.createElement('div');
+    var dialogElement = this._createHostElement();
     DOM.appendChild(DOM.query('body'), dialogElement);
 
     // TODO(jelbourn): Use hostProperties binding to set these once #1539 is fixed.
@@ -75,7 +76,7 @@ export class MdDialog {
 
     // First, load the MdDialogContainer, into which the given component will be loaded.
     return this.componentLoader.loadIntoNewLocation(
-        MdDialogContainer, elementRef, dialogElement).then(containerRef => {
+        MdDialogContainer, elementRef, `:document#${dialogElement.id}`).then(containerRef => {
       dialogRef.containerRef = containerRef;
 
       // Now load the given component into the MdDialogContainer.
@@ -101,12 +102,18 @@ export class MdDialog {
 
   /** Loads the dialog backdrop (transparent overlay over the rest of the page). */
   _openBackdrop(elementRef:ElementRef, injector: Injector): Promise<ComponentRef> {
-    var backdropElement = DOM.createElement('div');
+    var backdropElement = this._createHostElement();
     DOM.addClass(backdropElement, 'md-backdrop');
     DOM.appendChild(DOM.query('body'), backdropElement);
 
     return this.componentLoader.loadIntoNewLocation(
-        MdBackdrop, elementRef, backdropElement, injector);
+        MdBackdrop, elementRef, `:document#${backdropElement.id}`, injector);
+  }
+
+  _createHostElement() {
+    var hostElement = DOM.createElement('div');
+    hostElement.id = `mdDialog${_nextDialogId++}`;
+    return hostElement;
   }
 
   alert(message: string, okMessage: string): Promise {