refactor(render): cleanup access to native dom elements

BREAKING CHANGES:
- rename `ElementRef.domElement` to `ElementRef.nativeElement`
- add `Renderer.getNativeElementSync` to make the app side
  less dependent on the dom renderer.
- don’t use `ElementRef.nativeElement` in directives but
  use the methods on `Renderer` directly.
- Removed `ElementRef.setAttribute`. Use `Renderer.setElementAttribute` instead.

Closes #2712
Last part of #2476
Closes #2476

modules/angular2/src/services/ruler.ts

@@ -24,7 +24,7 @@ export class Ruler {
   constructor(domAdapter: DomAdapter) { this.domAdapter = domAdapter; }
 
   measure(el: ElementRef): Promise<Rectangle> {
-    var clntRect = <any>this.domAdapter.getBoundingClientRect(el.domElement);
+    var clntRect = <any>this.domAdapter.getBoundingClientRect(el.nativeElement);
 
     // even if getBoundingClientRect is synchronous we use async API in preparation for further
     // changes