cmd, common, node, rpc: move IPC into the node itself

cmd/geth/main.go

cmd/geth/monitorcmd.go

cmd/gethrpctest/main.go

cmd/utils/client.go

cmd/utils/flags.go

common/path.go

node/config.go

node/config_test.go

node/node.go

node/node_example_test.go

node/node_test.go

node/service_test.go

node/utils_test.go

rpc/json.go