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/debug.ts

@@ -1,2 +1,2 @@
 export * from './src/debug/debug_element';
-export {inspectDomElement, ELEMENT_PROBE_CONFIG} from './src/debug/debug_element_view_listener';
+export {inspectNativeElement, ELEMENT_PROBE_CONFIG} from './src/debug/debug_element_view_listener';