Implement TransportProtocol for a server

[mpapierski]

Implement a server for transport protocol.

In a similiar way as network_requests.rs were refactored out - For each endpoint defined It should check whether a specified channel exists, and then it should call correct method on the transport protocol implementation. So in the end guac_actix would define actual HTTP server, but the handlers will be called on the impl from guac_core. See #47 for more info regarding usefulness of guac_actix.