Prep for use in multi-extension-template

[tjcouch-sil]

Made adjustments to this template in order to make it able to be generated interchangeably from its own folder or from the multi-extension-template folder. Also some other improvements for consistency.

• Webpack now generates the main and types files in the same place in the dist folder to avoid great confusion
• Moved assets folder from being inside the public folder to being in root
• Moved manifest.json from being inside the public folder to being in root
• Synced formatting settings with core
• Added more template instructions to readme

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[irahopkinson]

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[lyonsil]

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