Move md-cell display logic to css
remove useless comment
update to warnings
Update path.py

change str formatting to repr representation.
allow --help and config_file classes to differ

override help_classes or config_classes
to allow them to differ from App.classes
only include kernel config in `--help` output

don't write it to a config file that won't be read
ipython_kernel gets its own config file
skip test_not_writable_ipdir if I can't create a non-writable dir

such as when running as root

just came across this running iptest in a docker container. This was the only test that failed.
Allow timeout and click callback
Add documentation to NotificationWidget methods
Add documentation to notification area
Small changes to notification widget
Add tests for notification area and widgets
Make Widget.views be an object indexed by view id
on_atomic_change -> on_some_change
Clarify stickiness of warning/danger notifications
Merge pull request #6549 from SylvainCorlay/some_update

on_atomic_change -> on_some_change
put back null gui hook for osx

`--gui osx` doesn't make sense on its own,
but it's called by `--matplotlib osx`,
which does.
run iptest in Dockerfile

and install sphinx with apt, since it's super slow
because of 2to3
Use some more informative asserts in inprocess kernel tests

Prompted by gh-6552 (but doesn't fix it)