refactor(docs): replace react-highlighjs with react-ace

[levithomason]

This PR replaces react-highlight with react-ace. Fixes a number of things:

• sets us up for having code editors in the docs (feat(docs): add component explorer #427)
• resolves the intermittent build failures due to autoit (a react-highlight dep)
• fixes JSX syntax highlighting
• added an "active" style to code examples that are showing their code

Before

After

[codecov-io]

Current coverage is 98.74% (diff: 100%)

Merging #525 into master will not change coverage

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  Files           107        107          
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  Hits           1732       1732          
  Misses           22         22          
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