Merge pull request #6578 from jtattermusch/add_bat_copyrights

examples/csharp/helloworld/generate_protos.bat

examples/csharp/route_guide/generate_protos.bat

src/csharp/build_packages.bat

src/csharp/buildall.bat

templates/src/csharp/build_packages.bat.template

test/distrib/csharp/build_vs2015.bat

tools/distrib/check_copyright.py

tools/run_tests/build_artifact_csharp.bat

tools/run_tests/post_tests_csharp.bat

tools/run_tests/pre_build_c.bat

tools/run_tests/pre_build_csharp.bat

vsprojects/build_plugins.bat

vsprojects/build_vs2010.bat

vsprojects/build_vs2013.bat

vsprojects/build_vs2015.bat

vsprojects/coapp/openssl/buildall.bat

vsprojects/coapp/zlib/buildall.bat