Add a command to connect to a remote REPL

[bbatsov]

inf-clojure already supports connecting to remote REPLs but the support is pretty lame as it involves setting the host and port in the command inf-clojure uses to start the REPL. It'd be way nicer if there was just an interactive command prompting you for a host and port and connecting to them. This bit of functionality should be pretty easy to implement.