chore(build): enable type-checking for TypeScript ES6 emit.

This requires delicate handling of type definitions which collide, because
we use TypeScript-provided lib.d.ts for --target=es5 and lib.es6.d.ts for
--target=es6.
We need to include our polyfill typings only in the --target=es5 case,
and the usages have to be consistent with lib.es6.d.ts.
Also starting with this change we now typecheck additional modules,
so this fixes a bunch of wrong typings which were never checked before.

Fixes #3178

modules/examples/src/web_workers/todo/index_common.ts

@@ -56,5 +56,5 @@ export class TodoApp {
     this.todoStore.list.forEach((todo: Todo) => { todo.completed = this.isComplete; });
   }
 
-  clearCompleted(): void { this.todoStore.removeBy((todo) => todo.completed); }
+  clearCompleted(): void { this.todoStore.removeBy((todo: Todo) => todo.completed); }
 }

modules/examples/src/web_workers/todo/services/TodoStore.ts

@@ -1,5 +1,5 @@
 import {Injectable} from 'angular2/angular2';
-import {ListWrapper} from 'angular2/src/facade/collection';
+import {ListWrapper, Predicate} from 'angular2/src/facade/collection';
 
 // base model for RecordStore
 export class KeyModel {
@@ -34,7 +34,7 @@ export class Store {
 
   remove(record: KeyModel): void { this._spliceOut(record); }
 
-  removeBy(callback: Function): void {
+  removeBy(callback: Predicate<KeyModel>): void {
     var records = ListWrapper.filter(this.list, callback);
     ListWrapper.removeAll(this.list, records);
   }