Review TransportServer interface

[flowersinthesand]

TransportServer consumes resource and produces ServerTransport. For example, HttpTransportServer consumes ServerHttpExchange and produces streaming transport and long polling transport. But, that's all. It is the only purpose of TransportServer.

• Interface name
  Server also consumes transport and produces socket but besides other functionalities like finding socket are also provided as Cettia server. On the other hand, TransportServer does not and should not provide such unnecessary features. In that sense, I feel TransportServer is awkward but couldn't find other proper name. Otherwise, we may need a general term for such interface.
• Maven artifact
  For those who want to use Cettia transport only e.g. to build custom protocol on top of Cettia transport layer, cettia-transport-server module should be separated from cettia-server module.