Session fixups

[cmdrk]

This PR ensures that serialization happens in the connection handler. It also specifically ensures that enet is handling disconnect callbacks properly.

• ow_session_util.erl
  • Do not serialize the session_pong message here
• ow_enet.erl
  • Properly handle disconnects.
  • Fix for serializing replies
• ow_websocket.erl
  • Ensure any replies are serialized
• ow_zone.erl
  • cleanup some TODOs