Rename client_config directory to client_channel.

BUILD

CMakeLists.txt

Makefile

binding.gyp

build.yaml

config.m4

gRPC-Core.podspec

grpc.gemspec

package.xml

src/core/ext/client_channel/README.md

src/core/ext/client_channel/channel_connectivity.c

src/core/ext/client_channel/client_channel.c

src/core/ext/client_channel/client_channel.h

src/core/ext/client_channel/client_channel_factory.c

src/core/ext/client_channel/client_channel_factory.h

src/core/ext/client_channel/client_channel_plugin.c

src/core/ext/client_channel/connector.c

src/core/ext/client_channel/connector.h

src/core/ext/client_channel/default_initial_connect_string.c

src/core/ext/client_channel/initial_connect_string.c