drop-in sockjs
add sockjs-tornado
update sockjs.tornado imports

for IPython.external imports
use SockJS instead of pure websockets
fix missed heartbeat message for sockjs
fix new cookie name for sockjs
Add joined IOPubAndShellHandler

Now only one SockJS connection is needed in the browser for both channels.
The previous single-channel connections remain available.
cookie message must not be empty

SockJS seems to ignore empty messages
update sockjs-tornado

to hash ed3ce990a71e9dea5f82c153429b051186062431
import ioloop from zmq, not tornado

in sockjs-tornado

tornado >= 2.5 makes a minor change in the IOLoop API,
so tornado.ioloop.PeriodicCallback >= 2.5 will not work with
IOLoop from pyzmq < 3.2.