chore(build): simplify and fix hmr

[levithomason]

I'm beginning to address some of the build issues. This PR:

• Fixes hot module reloading, the doc site actually reloads properly in dev now 🎉
• trims the install footprint by removing unnecessary react and babel plugins
• rewrites the gulpfile and tasks to plain node, no babel-register precompile

[codecov-io]

Current coverage is 100% (diff: 100%)

Merging #821 into master will not change coverage

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[levithomason]

@Semantic-Org/react-collaborators Aside from this PR, I also pushed some updates that affect how dependencies work. I suggest you rm -rf node_modules && npm i to get a fresh install. Not only are packages different, but the tree needs to be flattened for some of them.