Bug 1103120 - Part 1: Advertise server cert for authentication. r=past
Bug 1103120 - Part 2: Create ServerSocketConnection on accept. r=past

Extract the socket accept logic into a new object, in preparation for more
complex steps to handle authentication.  As a bonus, the new workflow ensures
that the TLS handshake is validated before handing the connection of to the
DebuggerServer.