shorten sessions IDs for now

* easier to read while debugging
add basic logging to session

* so I can see what's going on
send a sharejs type response to new sessions

* to help with debugging. I'll have to remove it once there's a generic
  way to hook a protocol into browserchannel
expand headers sent with chunked responses

* always include the date
* always include CORS
browser channel chunks start with a decimal byte count

* let the code responsile for the HTTP response prefix a decimal byte
  count as required by the HTTP spec for chunked responses
use noop's to keep the backchannel open