Implement smart readline completion in the interactive mode

[bengtmartensson]

• First, complete on the command names
• for commands with subcommands, like transmit, complete on the subcommands,
• for parameters, complete on the variable names
• Some parameters, like receiveFormat, takes values only in a small set, that can be completed upon.
• remotes and their contained commands can be completed on.

Good example of smart readline completion are found in oldharctoolbox.