Implement XOM style fixes for matcher
Implement XOM style fixes for matcher

Summary:
This is the first of a series of small fixes that will be applied to our Perseus widgets on phones.

Right now, I've gated these changes behind the `xomManatee` flag, which will only be enabled on
touch devices. After we resolve the beta, we may need to replace that flag with a `phoneStyles`
flag or something similar, if we want these small tweaks to only be active on touch devices.

On Asana @ https://app.asana.com/0/132409062806753/132845143650932.

Test Plan:
- Disable the `xomManatee` flag via local storage.
- Open up [this item](http://localhost:9000/#content=%7B%22question%22%3A%7B%22content%22%3A%22%5B%5B%E2%98%83%20matcher%201%5D%5D%5Cn%5Cn%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22matcher%201%22%3A%7B%22type%22%3A%22matcher%22%2C%22alignment%22%3A%22default%22%2C%22static%22%3Afalse%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22left%22%3A%5B%22%24x%24%22%2C%22%24y%24%22%2C%22%24z%24%22%5D%2C%22right%22%3A%5B%22%241%24%22%2C%22%242%24%22%2C%22%243%24%22%5D%2C%22labels%22%3A%5B%22test%22%2C%22label%22%5D%2C%22orderMatters%22%3Afalse%2C%22padding%22%3Atrue%7D%2C%22version%22%3A%7B%22major%22%3A0%2C%22minor%22%3A0%7D%7D%7D%7D%2C%22answerArea%22%3A%7B%22calculator%22%3Afalse%2C%22chi2Table%22%3Afalse%2C%22periodicTable%22%3Afalse%2C%22tTable%22%3Afalse%2C%22zTable%22%3Afalse%7D%2C%22itemDataVersion%22%3A%7B%22major%22%3A0%2C%22minor%22%3A1%7D%2C%22hints%22%3A%5B%5D%7D).
    - Verify that there are 8px between items in the right column.
    - Verify that the items in the left column are aligned with those in the right column.
    - Verify that there is 16px to the left and right of the two columns.

{F542381}

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Reviewers: benkomalo, david

Reviewed By: david

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D27784

ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus