Async client connect() method

[MaXaMaR]

Currently connect() method trashes the update thread. That makes handling multiple parallel connections troublesome. For example that may be done by separating calls to update() methods in two threads - first one handles the connecting clients and the second one handles send/recv updates. However I'm not sure how correct is it to handle all connect calls in one thread as latency was high when using single thread only (3-4s single thread vs 1-2ms two update threads). Overall it would be great if connect() was async too without all-time-polling connect-only handling thread that is always active in the profiler.

TcpConnection.java:77 socket.connect(remoteAddress, timeout); // Connect using blocking mode for simplicity.

[MaXaMaR]

It also postpones graceful shutdown

[payne911]

@MaXaMaR About your last comment: could a postponed graceful shutdown be a possible cause for the following issue? https://github.com/EsotericSoftware/kryonet/issues/142