Add JS config API
Fix punctuation
Use promising_ajax in config API
Actually define the module

I didn't forget something really obvious and important. Not at all.
Fix some other bugs
Merge pull request #6949 from minrk/kernel_created

fix event hookup for kernel changed
Merge pull request #6874 from takluyver/config-js-api

Add JS config API
add utils.get_url_param

I really cannot believe that we need to write this ourselves
allow kernel_name to be specified in url parameter
change kernel spec placeholder name to 'Kernel'
handle undefined settings in promising_ajax
Add kernel-select dropdown to new notebook button

most recent choice is remembered in localStorage
include current kernel name in new notebook dropdown