Issue 18: implement JSON-RPC API

Created the "rpc" command in the console_interface.py and added a similar
command in wallet_controller. Created the pass-thru which takes commands
like this:

python ngccc.py rpc <rpc command> <rpc command argument 1> <rpc command argument 2> ...

(e.g. "python ngccc.py rpc validateaddress 1EKPLQEeqpfnQjGeJ2T9HULMgSU7nfYhx8")