Add PHP Copyright

src/php/lib/Grpc/AbstractSurfaceActiveCall.php

src/php/lib/Grpc/ActiveCall.php

src/php/lib/Grpc/BaseStub.php

src/php/lib/Grpc/BidiStreamingSurfaceActiveCall.php

src/php/lib/Grpc/ClientStreamingSurfaceActiveCall.php

src/php/lib/Grpc/ServerStreamingSurfaceActiveCall.php

src/php/lib/Grpc/SimpleSurfaceActiveCall.php

src/php/lib/autoload.php

src/php/tests/generated_code/GeneratedCodeTest.php

src/php/tests/interop/interop_client.php

src/php/tests/unit_tests/CallTest.php

src/php/tests/unit_tests/CompletionQueueTest.php

src/php/tests/unit_tests/EndToEndTest.php

src/php/tests/unit_tests/SecureEndToEndTest.php

src/php/tests/unit_tests/TimevalTest.php

tools/distrib/check_copyright.py