Python source reorganization.

src/python/src/grpc/_adapter/_links_test.py

src/python/src/grpc/_adapter/_lonely_rear_link_test.py

src/python/src/grpc/_adapter/_low.py

src/python/src/grpc/_adapter/_low_test.py

src/python/src/grpc/_adapter/_proto_scenarios.py

src/python/src/grpc/_adapter/_server.c

src/python/src/grpc/_adapter/_server.h

src/python/src/grpc/_adapter/_server_credentials.c

src/python/src/grpc/_adapter/_server_credentials.h

src/python/src/grpc/_adapter/_test_links.py

src/python/src/grpc/_adapter/fore.py

src/python/src/grpc/_adapter/rear.py

src/python/src/grpc/_junkdrawer/__init__.py

src/python/src/grpc/_junkdrawer/math_pb2.py

src/python/src/grpc/_junkdrawer/stock_pb2.py

src/python/src/grpc/early_adopter/__init__.py

src/python/src/grpc/early_adopter/_face_utilities.py

src/python/src/grpc/early_adopter/implementations.py

src/python/src/grpc/early_adopter/interfaces.py

src/python/src/grpc/early_adopter/utilities.py