cleanup IPython handler settings

move settings to the tornado settings dict,
rather than a mixture of tornado settings and application references,
and application.ipython_app references.

removes any reference to application / ipython_app attributes in the handlers,
in favor of the tornado settings dict.
These were a massive pain for anyone who might want to re-use our handlers.
define clear_cookie on websocket handler

as a no-op
hook up tornado 3's loggers to our handlers
hook up proper loggers

use IPython logger as first choice, fall back on tornado logger
(for use in non-IPython apps).
remove unused zmqhttp
Merge pull request #3088 from minrk/nbsettings

cleanup IPython handler settings