feat(facade): add isMap method

modules/angular2/src/facade/lang.dart

@@ -26,6 +26,7 @@ bool isBlank(obj) => obj == null;
 bool isString(obj) => obj is String;
 bool isFunction(obj) => obj is Function;
 bool isType(obj) => obj is Type;
+bool isMap(obj) => obj is Map;
 
 String stringify(obj) => obj.toString();
 

modules/angular2/src/facade/lang.ts

@@ -75,6 +75,10 @@ export function isType(obj): boolean {
   return isFunction(obj);
 }
 
+export function isMap(obj): boolean {
+  return typeof obj === 'object' && obj !== null;
+}
+
 export function stringify(token): string {
   if (typeof token === 'string') {
     return token;