getlantern/lantern#2114 Added ability to run server unencrypted

Note - This still needs unit tests to be added to cover the plain-text scenario.

Note - this does not add unencrypted support to the client, since that will always be connecting to some sort of TLS server

Note - this change was made against the tcpproxying branch since that's coming to devel soon, and the structure of the server code is different from what's currently on devel.