Upgrade to netty 4.0.0

This pull-req changes vert.x to use netty 4.0.0 and so the new api under the hood.

Because of this I also removed all the websocket decoder/encoder in vert.x and just used what netty provided while still expose the same API to the end-user. 

@purplefox please review and once you feel comfortable with it I can squash and pull in.

Ps: Thanks to this I was able to spot some bugs in netty :)