Update qtip version, along with khan-site.css
Merge pull request #36219 from Khan/update-qtip

Update qtip version, along with khan-site.css
Fix into-mixed problem type

Close #36287.

Auditors: eater
Change pack.rb to be a filter, and add a make command for old functionality.

Summary:
Now pack.rb takes an html file from stdin (or it can be listed on the
commandline, using the magic of ARGF) and emits the 'packed' html
to stdout.  This makes it easier to use in a variety of contexts.

A new 'make pack' (or 'make packed') rule mimics the old behavior:
packing everything in exercises/ and putting it in exercises-packed/
but skipping files that are newer in exercises-packed/ (and thus
unchanged since the last pack run).

Style nit: read() doesn't take parens.

Emit all errors to stderr.

Test Plan:
Ran
  mv exercises-packed /tmp
  make pack
  diff -r exercises-packed /tmp/exercises-packed
to verify that the output is unchanged.  Then ran
  make pack
again and verified it's a noop.  Then ran
  rm exercises-packed/z*
  make pack
and verified it only re-made the z_scores* packages.  Then ran
  touch -t199001010000 exercises-packed/z*
  make pack
and verified it re-made the z_scores* packages (and nothing else).

Reviewers: eater, alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D995
Use a proper data-ensure to ensure nonsimilarity

Fixes #36508.
Decimals aren't acceptable as a rational answer...

Closes #36270.

Auditors: emily
Make a fallback of "0" actually work

jQuery .data() casts to a number if it looks like an number, and 0 is falsey.

Closes #36244.

Auditors: emily
Update css/khan-exercise.css

One missing semicolon.
Make update-khan-site.sh work with new combine.py script

Also update the sed regex to prevent it from emitting two consecutive slashes.
Fix typo in similar triangles 2 hints

Closes #36713.

Auditors: eater
Regenerate khan-site.css

Note that the last version seems to have a lot of duplicate css for
some reason.
Remove weird creation of empty file
Merge pull request #36645 from mikegee/patch-1

One missing semicolon in css/khan-exercise.css
Update khan-site.css yet again

Rerunning it gives me a huge diff, so I suspect the last one was generated
from an out of date website repo or something
Allow unsimplified to match acceptable formats

Closes #36987.

Auditors: eater
Merge pull request #36829 from Khan/update-qtip

Tweaks from review K91485
Add 3 chemistry exercises!

Test Plan: Tested locally and content reviewed on sandcastle by Jay Skipper

Reviewers: stephanie

Reviewed By: stephanie

Differential Revision: http://phabricator.khanacademy.org/D1010
Fix mobile device check for numeric answers.

Summary:
Current the user agent on the client side.

Causes the numeric keyboard to show up on questions with numeric answers.

Test Plan: * Changed User Agent to Nexus 7 using User Agent Switcher on Chrome Desktop. Saw input type=number in the inspector.

Reviewers: tom

Reviewed By: tom

Differential Revision: http://phabricator.khanacademy.org/D1013
Add visualizing derivatives exercise (WIP)

Summary: This is still a work in progress. Just want to get up on Sandcastle so folks can give design feedback!

Test Plan: Tested locally

Reviewers: eater

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D992
Revert "Fix mobile device check for numeric answers."

Un-break fractions (and presumably others) on Chrome, Mobile Safari.

This reverts commit 29f62ece6c11b725c87b32bc16b773e4bca7e827.