The complete move to MIT license (#115)

- headers in .js files
- update README and LICENSE year

Testing:

grep BSD, Patents, patents turned up nothing

lib/core/nav/SideNav.js

@@ -1,10 +1,8 @@
 /**
  * Copyright (c) 2017-present, Facebook, Inc.
- * All rights reserved.
  *
- * This source code is licensed under the BSD-style license found in the
- * LICENSE file in the root directory of this source tree. An additional grant
- * of patent rights can be found in the PATENTS file in the same directory.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
  */
 
 const React = require("react");
@@ -74,7 +72,7 @@ class SideNav extends React.Component {
     let localizedString;
     const i18n = translation[this.props.language];
     const sbTitle = metadata.sidebar_label;
-    
+
     if (sbTitle) {
       localizedString = i18n
         ? i18n["localized-strings"][sbTitle] || sbTitle