* More intention revealing than connecting on the first call to Connection#send
* Fixes that calls to Connection#send would attempt to open a connection when the WebSocket's state is CONNECTING

This change makes ping into a message type, which
makes the whole protocol a lot more consistent.

Also fixes hacks on the client side to make this all
work.

Added to aid in developing Action Cable, but isn't neccessary for production operation.

Without this, it's very easy to send messages over a subscription even before the
redis pubsub has been fully initialized.

Now we delay calling the subscription#connected method on the client side until we
receive a subscription confirmation message from the server.

 It was initially required, but support for the shorthand has been
 supported since sprockets 2.1. Eventually 4.x will only support the
 shorthand version. Just want to get new people using the prefer stuff
 ASAP.

This matches the server-side setup and is more consistent.