Catching Throwable instead of Exception.
Removed unneeded casting to DataFrame.
Refactored the send of the SETTINGS frame from the client.
It's now sent after a call to onPreface(), which has been moved to
the common interface Session.Listener (from ServerSession.Listener),
so that client applications can customize the SETTINGS to send to the
server.
Fixed off-by-one in counting the padding bytes.