Add license checker config and kokoro presubmit

`license-checker` is a tool that verifies each file has contains a permitted license header.

See https://github.com/ben-clayton/license-checker for more information.

Also add missing licenses to presubmit scripts.

kokoro/windows/presubmit.bat

@@ -1,3 +1,17 @@
+REM Copyright 2020 Google LLC
+REM
+REM Licensed under the Apache License, Version 2.0 (the "License");
+REM you may not use this file except in compliance with the License.
+REM You may obtain a copy of the License at
+REM
+REM     https://www.apache.org/licenses/LICENSE-2.0
+REM
+REM Unless required by applicable law or agreed to in writing, software
+REM distributed under the License is distributed on an "AS IS" BASIS,
+REM WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+REM See the License for the specific language governing permissions and
+REM limitations under the License.
+
 @echo on
 
 SETLOCAL ENABLEDELAYEDEXPANSION