feat(core): add support for ambient directives

Ambient directives can be configured when bootstraping an application.
Ambient directives can be used in every component of the application without
needing to explicitly list them.

modules/angular2/common.ts

@@ -0,0 +1,51 @@
+import {CONST_EXPR, Type} from './src/core/facade/lang';
+
+import {FORM_DIRECTIVES} from './src/core/forms';
+import {CORE_DIRECTIVES} from './src/core/directives';
+export * from './src/core/pipes';
+export * from './src/core/directives';
+
+/**
+ * A collection of Angular core directives that are likely to be used in each and every Angular
+ * application. This includes core directives (e.g., NgIf and NgFor), and forms directives (e.g.,
+ * NgModel).
+ *
+ * This collection can be used to quickly enumerate all the built-in directives in the `directives`
+ * property of the `@Component` or `@View` decorators.
+ *
+ * ### Example
+ *
+ * Instead of writing:
+ *
+ * ```typescript
+ * import {NgClass, NgIf, NgFor, NgSwitch, NgSwitchWhen, NgSwitchDefault, NgModel, NgForm} from
+ * 'angular2/angular2';
+ * import {OtherDirective} from './myDirectives';
+ *
+ * @Component({
+ *   selector: 'my-component',
+ *   templateUrl: 'myComponent.html',
+ *   directives: [NgClass, NgIf, NgFor, NgSwitch, NgSwitchWhen, NgSwitchDefault, NgModel, NgForm,
+ * OtherDirective]
+ * })
+ * export class MyComponent {
+ *   ...
+ * }
+ * ```
+ * one could import all the common directives at once:
+ *
+ * ```typescript
+ * import {COMMON_DIRECTIVES} from 'angular2/angular2';
+ * import {OtherDirective} from './myDirectives';
+ *
+ * @Component({
+ *   selector: 'my-component',
+ *   templateUrl: 'myComponent.html',
+ *   directives: [COMMON_DIRECTIVES, OtherDirective]
+ * })
+ * export class MyComponent {
+ *   ...
+ * }
+ * ```
+ */
+export const COMMON_DIRECTIVES: Type[][] = CONST_EXPR([CORE_DIRECTIVES, FORM_DIRECTIVES]);