Converts CM5 into CM6

[khanniie]

Fixes #issue-number

Changes:

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

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[raclim]

Thanks so much for your work on this—I think this overall feels really solid!

I did some manual testing, and everything seems to function as expected besides the elements that you've already noted as TODOs! I just had a small question in codemirror.js, but aside from that that this feels like it's in a great place to me!