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.


I'd rather not avoid to stay away from flag names stated as a negation.  "plaintext" might be more obvious for the case when we set/keep this at `false`.