Imports of log_client command

PathSynopsis
contextPackage context defines the Context type, which carries deadlines, cancellation signals, and other request-scoped values across API boundaries and between processes.
flagPackage flag implements command-line flag parsing.
fmtPackage fmt implements formatted I/O with functions analogous to C's printf and scanf.
github.com/google/trillianPackage trillian contains the generated protobuf code for the Trillian API.
google.golang.org/grpcPackage grpc implements an RPC system called gRPC.
timePackage time provides functionality for measuring and displaying time.