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.
proportional font-size when editing heading cells

@MinRK @takluyver and I had the idea to do this when we were discussing #6225.
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
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
require mistune 0.3.1

changed signatures
mv services/notebooks services/contents
rename notebooks service to contents service

minimal functional changes, committing because tests are passing.
teach contents service about non-notebook files
teach tree view about non-notebook files
add support and tests for uploading and saving regular files
test creating a directory with PUT
contents service review

- missed some s/notebook/file/ in docstrings
- manager doesn’t sort contents
support deleting empty directories

can’t copy directories
use contents manager to handle redirect of /notebooks -> /files

avoids 404 on /files for visiting a nonexistent notebook