cleanup: move DomAdapter from angular2/core into angular2/platform/common_dom

BREAKING CHANGE

Before

import {DomAdapter} from 'angular2/core';

After

import {DomAdapter} from 'angular2/platform/common_dom';

Closes #5370

modules/angular2/test/core/linker/dynamic_component_loader_spec.ts

@@ -24,7 +24,7 @@ import {Component, View, ViewMetadata} from 'angular2/src/core/metadata';
 import {DynamicComponentLoader} from 'angular2/src/core/linker/dynamic_component_loader';
 import {ElementRef} from 'angular2/src/core/linker/element_ref';
 import {DOCUMENT} from 'angular2/src/platform/dom/dom_tokens';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {ComponentFixture_} from "angular2/src/testing/test_component_builder";
 
 export function main() {

modules/angular2/test/core/linker/integration_spec.ts

@@ -22,7 +22,7 @@ import {
 } from 'angular2/testing_internal';
 
 
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {
   Type,
   isPresent,

modules/angular2/test/core/linker/projection_integration_spec.ts

@@ -20,7 +20,7 @@ import {
   tick
 } from 'angular2/testing_internal';
 
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 import {AppViewListener} from 'angular2/src/core/linker/view_listener';
 
 import {

modules/angular2/test/core/linker/query_list_spec.ts

@@ -14,7 +14,7 @@ import {MapWrapper, ListWrapper, iterateListLike} from 'angular2/src/facade/coll
 import {IS_DART, StringWrapper} from 'angular2/src/facade/lang';
 import {ObservableWrapper} from 'angular2/src/facade/async';
 import {QueryList} from 'angular2/src/core/linker/query_list';
-import {DOM} from 'angular2/src/core/dom/dom_adapter';
+import {DOM} from 'angular2/src/platform/dom/dom_adapter';
 
 interface _JsQueryList {
   filter(c: any): any;