Consolidate answer input box width CSS so it doesn't leak between exercises #FIXIT

Test Plan: Locally check each exercise/problem type still looks the same(ish)

Reviewers: alpert, cbhl

Reviewed By: cbhl

Differential Revision: http://phabricator.khanacademy.org/D2056
Adding Exercise Converting Fahrenheit to Celsius
Resolves #41067. Made question more clear about the requirement for an exact answer.
Merge pull request #41171 from shanem/issue-41067

Use the word "exact" in Area of a Circle. (Fixes: #41067)
Merge pull request #31746 from xymostech/add-case-insensitive-regex

Add case-insensitive flag to regex answer type
nit per review in pull request #31746

Auditors: alpert
Merge pull request #38817 from steveKapturowski/master

Add Implicit Differentiation exercise.
Merge pull request #40939 from mwyllie/binomialExpansionHints

Add binomial expansion exercise by beneater and mwyllie.
Fix nits in Binomial Expansion.

Auditors: eater, emily
localMode instead of testMode

Rename testMode to localMode in the spirit of pull request #13413.

Auditors: eater, alpert
Merge pull request #24773 from petercollingridge/conseq_sum

Add Integer Sum exercise.
Merge pull request #39755 from davemajor/composite-shapes

New exercise: Rectangle Perimeter 2
Rename Rectangle Perimeter 2 to Interesting Perimeter Problems.
Update title element in Interesting Perimeter Problems.

Auditors: eater, alpert
Merge pull request #39732 from Helpsypoo/master

New hints for age_word_problems
Revert "Resolves #41067. Made question more clear about the requirement for an exact answer."

This reverts commit fe2cb56c3fc9992ae401059418f4db632e1c4039.

Auditors: eater, alpert
Binomial Expansion: More MathJax, and make it fit in the space better.

Addresses feedback in 1abed9801cd925074cf7872a61ed3cb6cd6abb94 on GitHub.

Auditors: eater
Revert "Merge pull request #38817 from steveKapturowski/master"

This reverts commit 9ec49bae13704b79cd3df9992d8b087d9e08bf0c, reversing
changes made to 9fd52ad4ac7cd922b6733dd8ce3a1c6ddad19063.

Will work on the hints a bit more and bring it back when it's ready.

Auditors: eater, alpert
Revert graphie-geometry changes for now.

Auditors: eater, alpert
Binomial Expansion: Avoid long problems that don't fit horizontally.

Auditors: eater