Render a simplified demo closer to what currently appears in webapp
Render a simplified demo closer to what currently appears in webapp

Summary:
Render an ItemRenderer instance without all of the chrome that was
around it before.  This will make it easier to implement that style
changes we'll need for KaTeX, tables, images, and typography.  The
changes for those items will come in following diffs.  I've also
introduced a localStorage flag for enabling/disabling this rendering.
The reason why I went with localStorage is that parts of the perseus
demo rely on the URL being in a specific format for routing purposes
and passing content to the rendered view.

__before__
{F541734}

__after__
{F541733}

Test Plan:
- load http://localhost:9000/?renderer#content=%7B%22question%22%3A%7B%22content%22%3A%22Hello%2C%20world%21%5Cn%5Cn%24x%20%3D%205%24%5Cn%5CnGoodbye%5Cn%5CnSee%20you%20later%5Cn%5Cn%5B%5B%E2%98%83%20expression%201%5D%5D%5Cn%5Cn%22%2C%22images%22%3A%7B%7D%2C%22widgets%22%3A%7B%22expression%201%22%3A%7B%22type%22%3A%22expression%22%2C%22alignment%22%3A%22default%22%2C%22static%22%3Afalse%2C%22graded%22%3Atrue%2C%22options%22%3A%7B%22answerForms%22%3A%5B%5D%2C%22buttonSets%22%3A%5B%22basic%22%5D%2C%22functions%22%3A%5B%22f%22%2C%22g%22%2C%22h%22%5D%2C%22times%22%3Afalse%7D%2C%22version%22%3A%7B%22major%22%3A1%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
- run 'localStorage.xomManatee = true' in the console
- reload
- see the new rendering of the exercise

Reviewers: emily, charlie

Reviewed By: emily

Subscribers: david, jared

Differential Revision: https://phabricator.khanacademy.org/D27560

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