exit python evaluators by calling kill on the underlying kernel.  but needs  new nginx rules due to new form of URL on these REST calls (they are actually DELETEs)

Conflicts:
	plugin/ipythonPlugins/src/dist/python3/python3.js
node: Implement noop exit() route to prevent browser error.
bunsen:  Allow window message to close notebook.
bunsen:  Remove unused bunsen menu reference.
bunsen:  When closing a notebook, send msg to bunsen to close iframe.

Also, don't redirect to control panel - that is not used for bunsen.
Merge pull request #947 from twosigma/mf/bunsen_cherry_pick_memfix

Mf/bunsen cherry pick memfix