Overhaul license comments and file annotations

* Updates all Copyright years to 2015.
* Adds licenses annotations to all JS.
* Makes all licenses identical to avoid repeated appearance in the
  compiled output.
* Drops fileoverview annotations, which do not affect docs output.
* The linter still requires fileoverview on externs.

This patch required a newer closure compiler, since the previous
version we used had a bug regarding license annotations that caused
the license comment block to appear in the output once per file
regardless of uniqueness.

Change-Id: I2e9272db680cba7ecc4613d97f1d3a94ac2244cc

lib/util/string_utils.js

@@ -1,5 +1,6 @@
 /**
- * Copyright 2014 Google Inc.
+ * @license
+ * Copyright 2015 Google Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -12,8 +13,6 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
- *
- * @fileoverview String utility functions.
  */
 
 goog.provide('shaka.util.StringUtils');