ensure that one of the numbers has a imaginary component

example: [adding_and_subtracting_complex_numbers.html?seed=120](http://sandcastle.khanacademy.org/media/castles/Khan:master/exercises/adding_and_subtracting_complex_numbers.html?seed=120&problem=0&debug)
consistent punctuation

end sentence with a punctuation
add missing closing span tag, fix: #58083
Change answer type to regex
Use expression editor for complex number questions
Remove complexRegex function as it's not needed any more
Put the line height on the math holders

Summary: If we put line-heights on things inside, sometimes it overrides
the line-height of the math itself (which messes things up). Fixes
T1280

Auditors: alpert
Merge pull request #58394 from mauk81/patch-1

add missing closing span tag, fix: #58083
Merge pull request #58393 from mauk81/patch-4

consistent punctuation
Add a curvy arrow widget.

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3319
Fix issue reporting

Fixes #58404. Can't have nested <form> elements in HTML... :(

Auditors: jakesandlund

CC: eater
Make multiplying polynomials choices a bit better

Fixes Google Code issue #20988.

Auditors: emily
Fix line height in creating_box_and_whisker_plots

Auditors: emily
Make MathJax colors work properly again

Test Plan:
Open scaling_vectors on live site, see colored arrow labels.

Auditors: eater
Fix `hundredths` spelling

Auditors: peter
Update katex

Auditors: emily
Make piechart accept a final stroke color.

Summary: Also works with more than two divisions.

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3360
Consistentize paren sizing in midpoint formula

Auditors: eater
Add curly brace graphie helper.

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D3347
Fix radio for none of the above

Summary:
When "none of the above" is selected, and we're missing a single
choice, add in "none of the above" as an answer, instead of dying. Fixes T1288.

Test Plan:
Open a question with 4 choices and data-show=5, data-none="true". See that it
adds back in "none of the above" as an answer. Also, see that the tests work.

Reviewers: alpert

Reviewed By: alpert

Maniphest Tasks: T1288

Differential Revision: http://phabricator.khanacademy.org/D3374