WIP React-less HiGlass-less Gosling

[sehilyi]

This is a PR of @etowahadams's fork that tries to get rid of HiGlass and React dependencies. Not yet ready to merge.

• Etowah's comment of things left

• More extensive testing of the new renderer. It seems to work well for the examples in the editor, but I'm sure we'll find more bugs. We have ways to comprehensively test certain aspects of the spec but not all.
• React API: I implemented a basic GoslingComponent but it doesn't have all of the features of the current component. I don't think this will be too difficult though.

• Etowah's note on potential improvements explanation.md

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Fix # Toward #

Change List

Checklist

• [ ] Ensure the PR works with all demos on the online editor
• [ ] Unit tests added or updated
• [ ] Examples added or updated
• [ ] Documentation updated (e.g., added API functions)
• [ ] Screenshots for visual changes (e.g., new encoding support or UI change on Editor)