send SOCKS-DISCONNECTED message as datachannel text payload
fix socks disconnection path all the way through netclient remote socket. fix #20
send NET-DISCONNECTED as text payload over datachannel from remote side
tcp disconnection event only on remote disconnect. fix #23
tidy netclient disconnect and close
fix bidirectional error clashes
tidy tcp error handling and close vs disconnect
Merge pull request #37 from uProxy/disconnect

disconnections - end-to-end works both ways