One-sided money connections

[emschwartz]

STREAM should work even if only one side is capable of sending money. Right now the connection will error out, however, if it is unable to send the first test packet. We should make it work under these conditions by going into some kind of "receive-only" mode.

[emschwartz]

We could do this by adding a config option like receiveOnly: true to both the client and the server. If that is set, it would not try to establish the exchange rate (though the client would need to send a test packet to communicate its address), and it would throw an error if the user tries to send money.