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
Handle 'deletable' cell metadata
Add tests for undeletable cells
Make cell be undeletable ONLY when metadata is explicitly false
Fix tests
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
Properly mock winreg functions for test

Fixes a lot of test failures on Python 3.4 on Windows, caused by
importlib trying to use our mocked out winreg functions when
reload(path) was called.
Make Widget.views be an object indexed by view id
Clarify stickiness of warning/danger notifications
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.