Merge pull request #4803 from y-p/PR_ipython_directive_cython

BUG: fix cython magic support in ipython_directive
Merge pull request #4832 from minrk/formatter-not-implemented

allow NotImplementedError in formatters
mv kerneljs_test to kernel_test
Merge pull request #4847 from Carreau/js-kernel-info

add js kernel_info request
Merge pull request #4826 from Carreau/no-html

some $.html( -> $.text(
Fixed bug in throttling code.
Fixed some more example files (see list below)...

Export As (nbconvert).ipynb
File Upload Widget.ipynb
Nonblocking Console.ipynb
index.ipynb
Updated cell numbering in console example.
Prevent TextBox from blurring unless explicity by user.
test traceback offset for %run and script
Update URL for Lawrence Hall of Science webcam image

Closes gh-4752

I also reran the notebook in order, so all the prompt numbers have
changed.

Also, update example to use IFrame class, and fix embedded video on Py 3
check the static path for build and install locations

allows packages to run the tests during package build and install time
where the two file locations might be split.
use DEFAULT_STATIC_FILES_PATH to find css files

get_ipython_package_dir() does not necessarily contain the files, e.g.
in distribution packages which share files with python3 in a different
folder.
Merge pull request #4858 from minrk/execfile-offset

fix tb_offset when running a file
Merge pull request #4868 from juliantaylor/static-path-fixes

Static path fixes
Simplified variable inspector example
Fixed bug that prevented popup widget from displaying
Removed D3 and Widget Tester examples for now, until they are fixed..
removed sehll=True
Merge pull request #4867 from takluyver/lhos-img-url

Update URL for Lawrence Hall of Science webcam image