deleting a comm now unregisters the comm. unrehistering the comm does not close it anymore
decoupling the comm lifetime from the widget lifetime
Remove $el_to_style from the widget javascript code; '' now defaults to this.$el

This seems to make it easiest to select the top-level element.  An alternative is to use special syntax for top-level elements, like in https://github.com/ipython/ipython/pull/6185

This will be followed up by other fixes that let the user set specific common properties of different elements.

This change also adds the .addBack() call, which means that nonempty selectors now apply to this.$el and its descendants, rather than just the descendants of this.$el.
comm_manager.comms correspond to the open comms.
unregister and register both take comm as argument
bad call and missing call to unregister_comm
close() already unregisters the comm
del Widget.widgets[seld.model_id] in close rather than in __del__
proportional font-size when editing heading cells

@MinRK @takluyver and I had the idea to do this when we were discussing #6225.
Fixed pandoc version detection.
Fix js-tests for new default selector logic.
appropriate heading level when loading from JSON
match font family when editing heading cells
fix more style consistencies
setting _comm to None
Merge pull request #6216 from SylvainCorlay/comm-unregister

Unregistering comms in Comm Manager
Merge pull request #5 from jdfreder/css-top-default

Fix js-tests for new default selector logic.
Fix qtconsole input prompt accounting

- Ensure prompt text is flushed after showing
- Ensure prompt position is adjusted when reading input
- Keep pending text to insert only when inserting at end

This fixes `ipdb>` input prompts when debugging a file
in qtconsole.
fix inline/block invocation with mistune
Merge pull request #6247 from minrk/mistune

fix inline/block invocation with mistune