i2ptunnel: Refactor UDPTunnel, Streamr, and SOCKS UDP for I2CP ports

- Add fromPort and toPort to Sink interface (breaking API change)
- Change cache maps from Destination to I2PSocketAddress to include port
- Accept host:port for destination in Streamr Client, use port
  as toPort in pinger
- Change to muxed listener in I2PSource, only listen for
  specified protocols
- Eliminate thread and queue in I2PSource, process messages inline
  in the listener
- Add support for handling both repliable and raw datagrams in
  a single I2PSource instance
- Remove verify option from I2PSource and I2PTunnelUDPServerBase,
  always verify repliable datagrams
- Add getPort() method to UDPSource
- Add a constructor to UDPSink to pass in an existing DatagramSocket
- Change I2PTunnelUDPClientBase to receive both repliable and raw
- Change SOCKSUDPTunnel reply handling strategy to key on I2CP toPort;
  remove ReplyTracker; the tunnel would not have worked before, because
  it expected raw replies only but MultiSink required a destination
  to look up where to forward the reply.
- Mark SOCKSUDPTunnel as preliminary; note lack of support
  for raw replies; untested
- Change Streamr Client Pinger to support fromPort
- Change Streamr Server to remember fromPort in subscriptions
  and use it as toPort in data stream
- Move fields to top of classes for sanity
- Cleanups and log tweaks