Modularized coloring of interactive2, transformer, and interactive-graph items

Summary:
Previously, coloring was done with hard-coded values (i.e., KhanUtil.BLUE), and some items
were colored differently than others. Now, the INTERACTABLE, NON_INTERACTABLE, and INTERACTING
colors are defined in ke/utils/math.js, and all interactive items in src are styled accordingly.
Note that these changes depend on D9800.

Test Plan:
- Run Perseus.
- Check out all these [interactive widgets](http://localhost:9000/test.html#content=%7B%22question%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20transformer%201%5D%5D%5Cn%5B%5B%E2%98%83%20transformer%202%5D%5D%5Cn%5B%5B%E2%98%83%20number-line%201%5D%5D%5Cn%5B%5B%E2%98%83%20interactive-graph%201%5D%5D%5Cn%5B%5B%E2%98%83%20interactive-graph%202%5D%5D%5Cn%5B%5B%E2%98%83%20interactive-graph%203%5D%5D%5Cn%5B%5B%E2%98%83%20plotter%201%5D%5D%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22transformer%201%22%3A%7B%22type%22%3A%22transformer%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22starting%22%3A%7B%22shape%22%3A%7B%22type%22%3A%5B%22circle%22%5D%2C%22coords%22%3A%5B%5B4%2C0%5D%2C%5B-4%2C4.898587195273712e-16%5D%5D%2C%22options%22%3A%5B%7B%7D%5D%7D%2C%22transformations%22%3A%5B%5D%7D%2C%22graphMode%22%3A%22interactive%22%2C%22listMode%22%3A%22dynamic%22%2C%22tools%22%3A%7B%22translation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%7D%7D%2C%22rotation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coord%22%3A%5B-5%2C4%5D%7D%2C%22reflection%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coords%22%3A%5B%5B2%2C-4%5D%2C%5B2%2C2%5D%5D%7D%2C%22dilation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coord%22%3A%5B6%2C6%5D%7D%7D%2C%22drawSolutionShape%22%3Atrue%2C%22gradeEmpty%22%3Afalse%2C%22graph%22%3A%7B%22range%22%3A%5B%5B-10%2C10%5D%2C%5B-10%2C10%5D%5D%2C%22step%22%3A%5B1%2C1%5D%2C%22markings%22%3A%22grid%22%2C%22labels%22%3A%5B%22x%22%2C%22y%22%5D%2C%22backgroundImage%22%3A%7B%22url%22%3Anull%2C%22scale%22%3A1%2C%22bottom%22%3A0%2C%22left%22%3A0%7D%2C%22showProtractor%22%3Afalse%2C%22showRuler%22%3Afalse%2C%22rulerLabel%22%3A%22%22%2C%22rulerTicks%22%3A10%2C%22gridStep%22%3A%5B1%2C1%5D%2C%22snapStep%22%3A%5B0.5%2C0.5%5D%7D%2C%22version%22%3A1.2%2C%22correct%22%3A%7B%22transformations%22%3A%5B%7B%22center%22%3A%5B-5%2C4%5D%2C%22angleDeg%22%3A210%2C%22type%22%3A%22rotation%22%7D%5D%2C%22shape%22%3A%7B%22type%22%3A%5B%22circle%22%5D%2C%22coords%22%3A%5B%5B-14.794228634059941%2C2.9641016151377744%5D%2C%5B-7.866025403784436%2C6.964101615137752%5D%5D%2C%22options%22%3A%5B%7B%7D%5D%7D%7D%7D%7D%2C%22transformer%202%22%3A%7B%22type%22%3A%22transformer%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22starting%22%3A%7B%22shape%22%3A%7B%22type%22%3A%5B%22angle%22%5D%2C%22coords%22%3A%5B%5B4.5%2C5%5D%2C%5B-5%2C7%5D%2C%5B-3.5%2C-4%5D%5D%2C%22options%22%3A%5B%7B%22reflex%22%3Afalse%7D%5D%7D%2C%22transformations%22%3A%5B%5D%7D%2C%22graphMode%22%3A%22interactive%22%2C%22listMode%22%3A%22dynamic%22%2C%22tools%22%3A%7B%22translation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%7D%7D%2C%22rotation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coord%22%3A%5B1%2C6%5D%7D%2C%22reflection%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coords%22%3A%5B%5B2%2C-4%5D%2C%5B2%2C2%5D%5D%7D%2C%22dilation%22%3A%7B%22enabled%22%3Atrue%2C%22required%22%3Afalse%2C%22constraints%22%3A%7B%22fixed%22%3Afalse%7D%2C%22coord%22%3A%5B6%2C6%5D%7D%7D%2C%22drawSolutionShape%22%3Atrue%2C%22gradeEmpty%22%3Afalse%2C%22graph%22%3A%7B%22range%22%3A%5B%5B-10%2C10%5D%2C%5B-10%2C10%5D%5D%2C%22step%22%3A%5B1%2C1%5D%2C%22markings%22%3A%22grid%22%2C%22labels%22%3A%5B%22x%22%2C%22y%22%5D%2C%22backgroundImage%22%3A%7B%22url%22%3Anull%2C%22scale%22%3A1%2C%22bottom%22%3A0%2C%22left%22%3A0%7D%2C%22showProtractor%22%3Afalse%2C%22showRuler%22%3Afalse%2C%22rulerLabel%22%3A%22%22%2C%22rulerTicks%22%3A10%2C%22gridStep%22%3A%5B1%2C1%5D%2C%22snapStep%22%3A%5B0.5%2C0.5%5D%7D%2C%22version%22%3A1.2%2C%22correct%22%3A%7B%22transformations%22%3A%5B%5D%2C%22shape%22%3A%7B%22type%22%3A%5B%22angle%22%5D%2C%22coords%22%3A%5B%5B4.5%2C5%5D%2C%5B-5%2C7%5D%2C%5B-3.5%2C-4%5D%5D%2C%22options%22%3A%5B%7B%22reflex%22%3Afalse%7D%5D%7D%7D%7D%7D%2C%22number-line%201%22%3A%7B%22type%22%3A%22number-line%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22correctRel%22%3A%22gt%22%2C%22isInequality%22%3Atrue%2C%22range%22%3A%5B0%2C10%5D%2C%22labelRange%22%3A%5Bnull%2Cnull%5D%2C%22divisionRange%22%3A%5B1%2C10%5D%2C%22labelStyle%22%3A%22decimal%22%2C%22labelTicks%22%3Atrue%2C%22numDivisions%22%3A5%2C%22tickStep%22%3Anull%2C%22snapDivisions%22%3A2%2C%22correctX%22%3Anull%2C%22initialX%22%3Anull%7D%7D%2C%22interactive-graph%201%22%3A%7B%22type%22%3A%22interactive-graph%22%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22step%22%3A%5B1%2C1%5D%2C%22backgroundImage%22%3A%7B%22url%22%3Anull%2C%22scale%22%3A1%2C%22bottom%22%3A0%2C%22left%22%3A0%7D%2C%22markings%22%3A%22graph%22%2C%22labels%22%3A%5B%22x%22%2C%22y%22%5D%2C%22showProtractor%22%3Atrue%2C%22showRuler%22%3Atrue%2C%22rulerLabel%22%3A%22%22%2C%22rulerTicks%22%3A10%2C%22range%22%3A%5B%5B-10%2C10%5D%2C%5B-10%2C10%5D%5D%2C%22gridSt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Reviewers: jack

Reviewed By: jack

Subscribers: marcos, eater

Differential Revision: http://phabricator.khanacademy.org/D9803