Implement LongPolling for Java client

[mikaelm12]

We currently only have support for WebSockets in the Java client. We should look at adding support for LongPolling as our next transport.

[mikaelm12]

I finished most of the functionality for this but it still needs tests. Because of some other higher priority things I'm gonna push this to 3.0.0 preview 3

[mikaelm12]

Done here 3d3ad96