Change "percent" answer type to interpret answer key as a decimal; accept percent in independent_probability Fix #37553

Test Plan: Ran `grep percent exercises/* | grep data-forms` to find all exercises using the percent data-form and tested several questions of each such problem type

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D1046
Use integer data forms on All the Exercises!

Summary:
Okay, not all of them. But a lot of them.

Use number field on Changing Decimals to Percents.

Use integer data form for Converting Between Point Slope and Slope Intercept.

Use type=number fields on Converting Between Point Slope and Standard Form.

Use integer data form in Domain and Range of a Function 0.5.

Use integer data form in EQuation of a Circle 1, 2

Use integer data form on Equation of an Ellipse.

Use integer, decimal data forms for Inscribed Angles 1, 2, 3

Use integer data form on Matrix Addition and Subtraction.

Use integer data forms for Matrix Dimensions.

Use integer data forms on Matrix Transpose.

Use integer data forms for Measuring Angles.

Use integer data form on Multiplying a Matrix by a Matrix.

Use integer data form on Multiplying a Matrix by a Vector.

Use integer, decimal data forms on Multiplying and Dividing Scientific Notation.

Use integer, decimal data forms on Multiplying Complex Numbers.

Use integer data form in One Step Equations.

Use integer data form in Perimeter 1.

Use integer data form in Perimeter of Squares and Rectangles.

Use integer data form in Pile Patterns.

Use integer, decimal data forms in Plugging in Values.

Use integer data form for Quadrilateral Angles.

Use integer and decimal data forms for Range of a Function.

Use integer data form for Reading Bar Charts 1.

Use integer, decimal data forms for Reading Line Charts 1.

Allow decimal data form for Reading Pictograms 2.

Use integer data form for Reading Tables 1,2.

Use integer, decimal data forms on Scientific Notation.

Use integer data form in Simplifying Expressions with Exponents.

Use integer data form in Solid Geometry.

Use integer, decimal data forms with Square Roots.

Use integer data form with Square Roots 2.

Use integer data forms with Scalar Matrix Multiplication.

Use integer data form on Telling Time 0.5

Test Plan: locally

Reviewers: tom, eater, stephanie

Reviewed By: eater

Differential Revision: http://phabricator.khanacademy.org/D1048
Don't ask questions with -1i as part of the answer

People were typing [-]i instead of [-1]i. This is a hacky workaround.
This also makes [ ]i equal i instead of 0i.

Fix #38028