chore: improve angular2.d.ts file

- support ambient and import format for .d.ts

docs/dgeni-package/templates/angular2/angular2.d.ts.template.html

@@ -9,11 +9,14 @@
 interface List<T> extends Array<T> {}
 interface Map<K,V> {}
 interface StringMap<K,V> extends Map<K,V> {}
-interface Type {}
+declare type Type = ng.Type;
 
-declare module "angular2/angular2" {
+declare module ng {
   type SetterFn = typeof Function;
   type int = number;
+  interface Type extends Function {
+    new (...args);
+  }
 
   // See https://github.com/Microsoft/TypeScript/issues/1168
   class BaseException /* extends Error */ {
@@ -22,4 +25,8 @@ declare module "angular2/angular2" {
     toString(): string;
   }
 }
-{% endblock %}
+{% endblock %}
+
+declare module "angular2/angular2" {
+  export = ng;
+}