Adding message forward capability to vertx-core

Simple functionality for message forwarding. Note, this will probably require a bit more work, but for now the basic functionality is in place. See MessageTest unit test for how it works.
True. I may be hung up on the JMS days where certain status variables in regards to messages were important (redelivered etc). I can't see it being that much of a bloat, but I am happy to remove it if you think it's best. I can go either way. I see some value in the flag, but since this behavior is still fairly new and no one has asked for it yet, I don't have a problem with removing it either.