When a preset is activated fire "preset_activated" event.
On "preset_activated" event, update the value of the maintoolbar select element that lists celltoolbar presets.
When a preset is registered after notebook is loaded, active it if needed.
Make sure that celltoolbars are hidden
when a notebook without "celltoolbar" entry in metadata is loaded.
remove Firefox-specific CSS workaround

The bug being worked around appears to be fixed either in CodeMirror or Firefox (tested with FF 29).

Importantly, the workaround appears to *introduce* incorrect behavior

closes #5192
closes #5364
Pass Windows interrupt event to kernels as an environment variable

This allows third party kernels to use our interrupt mechanism on
Windows.

Closes gh-5840
ensure load_connection_file works after self.session is created

only write to config if self.session hasn’t been instantiated,
otherwise write to session attrs.
build new Session auth when either key or scheme changes
add Session to ConnectionFileMixin

it’s used in a few places, so it doesn’t make sense for subclasses to lack it
ConnectionFileMixin is a LoggingConfigurable
test loading connection file after instantiating Session
Remove blank lines from <pre> blocks in nbconvert
Merge pull request #5856 from notsimon/master

Remove blank lines from <pre> blocks in nbconvert
Merge pull request #5845 from takluyver/windows-interrupt-envvar

Pass Windows interrupt event to kernels as an environment variable
Merge pull request #5843 from minrk/ff-css

remove Firefox-specific CSS workaround
add ownership to AsyncResult objects

An AsyncResult with owner=True will pop results and metadata, instead of get.
This should result is reduced memory growth on the Client.

AsyncResults created by apply, get_result, etc. have owner=True,
so this should help most cases.
update displaypub.publish signature in AsyncResult
Merge pull request #5784 from minrk/parallel-own-results

add ownership to AsyncResult objects
Skip qtconsole help test if no X11
Merge pull request #5863 from takluyver/skip-qt-help-test-nox

Skip qtconsole help test if no X11
Rework Latex test for nbconvert Python API

Also, skip it if pandoc is not available
Make test robust against differences in line endings

git on Windows can change line endings on checkout, which was leading to
a test failure.