Limit latex equations to page width.
Fixed latex template to support multicol w/ adjustbox.
update hmac signature comparison

see https://docs.python.org/2/library/hmac.html#hmac.compare_digest
support Python older than 2.7.7
minor cleanup
warn users running older versions of Python
correction in widget.js
one more bit
send ping every 30 seconds to keep websockets alive
move some responsive bootstrap transitions

- `-md-` puts the transition at 970px
- `-sm-` puts the transition at 768px

I moved most of the `md` transitions to `sm`,
which seems more reasonable.
I also moved the cluster list to `xs` because
the columns will never be wider than a dozen or so characters.
update comment

@ivanov is making the commit, but Kyle helped compose it, so he gets
points! Everything is awesome when you're part of a team!
Merge pull request #6114 from ivanov/update-digest-api

update hmac signature comparison
minor tweak to git hooks

- fix PREVIOUS_HEAD when run as git-merge
- catch fab css failure
Introduce info/warning/danger to notification area

Add corresponding style.

Should fix #5984

Error when (auto)saving and things along should stand out in the
UI for the user to investigate the reason as soon as possible not to
loose work later.
Merge pull request #6206 from minrk/git-hooks

minor tweak to git hooks
Allow switching kernel from the notebook UI
Change displayed kernel name when our session is started
Style kernel name
Line dropdown up on RHS of kernel name
Store kernelspec in notebook metadata on change