share code between zmq channel handlers
add stdin channel to NotebookApp
specify socket identity from kernel.js

required for stdin routing
add stdin to notebook

dumb / gross / ugly jQuery modal dialog for now,
but it works!
flush stale messages on stdin channel prior to raw_input
use inline raw_input instead of a dialog
clear_login_cookie is a no-op for websocket handlers

there's no cookie to clear, and it will raise on tornado 3.