feat: introduce Title service

Closes #612

Closes #900

modules/angular2/src/dom/browser_adapter.dart

@@ -173,6 +173,10 @@ class BrowserDomAdapter extends DomAdapter {
       document.implementation.createHtmlDocument('fakeTitle');
 
   HtmlDocument defaultDoc() => document;
+  String getTitle() => document.title;
+  void setTitle(String newTitle) {
+    document.title = newTitle;
+  }
   bool elementMatches(n, String selector) =>
       n is Element && n.matches(selector);
   bool isTemplateElement(Element el) =>

modules/angular2/src/dom/browser_adapter.es6

@@ -215,6 +215,12 @@ export class BrowserDomAdapter extends DomAdapter {
   defaultDoc() {
     return document;
   }
+  getTitle() {
+    return document.title;
+  }
+  setTitle(newTitle:string) {
+    document.title = newTitle;
+  }
   elementMatches(n, selector:string):boolean {
     return n instanceof HTMLElement && n.matches(selector);
   }

modules/angular2/src/dom/dom_adapter.js

@@ -201,6 +201,12 @@ export class DomAdapter {
   defaultDoc() {
     throw _abstract();
   }
+  getTitle() {
+    throw _abstract();
+  }
+  setTitle(newTitle:string) {
+    throw _abstract();
+  }
   elementMatches(n, selector:string):boolean {
     throw _abstract();
   }