Prevent re-bundling WordPress packages

[westonruter]

• Eliminate re-bundling of @wordpress/dom-ready and @wordpress/i18n to instead rely on existing bundles if available. Ensure both are marked as devDependencies.
• Include new standalone bundles of @wordpress/dom-ready and @wordpress/i18n if not available (e.g. in WordPress 4.9 without Gutenberg).
• Eliminate use of JSHint to avoid having to maintain duplicate duplicate linter as ESLint.

The @wordpress/dom-ready package is bundled with both WordPress 5.0 and Gutenberg as wp-dom-ready, so we should use it.

Also, @wordpress/i18n is not even used in the project anymore, so we don't need it at all.

Problem: If on 4.9 and Gutenberg is not installed, then we need to polyfill wp-dom-ready with jQuery.ready(). Nevertheless, we are currently depending on wp-i18n even though it may not be available either. So we might need to make the plugin require WordPress 5.0 or WordPress 4.9 with Gutenberg as the minimum version. Or perhaps in that case we should still bundle those dependencies as separate scripts that we register? If we want to support 4.9 without Gutenberg, then I suppose this is what we'd have to do. @felixarntz thoughts?

Closes #1763.

[felixarntz]

@westonruter Couldn't we bundle the wp-i18n and wp-dom-ready scripts in compiled versions and register them if they aren't yet available (by core)? I think that's the least error-prone solution, doesn't require too many changes. Whenever we decide to drop 4.x support, we can remove them without further change.

[westonruter]

@felixarntz this is ready to go!

[felixarntz]

Two minor questions, otherwise good to go.

[felixarntz]

I might miss something, but shouldn't this use wp.domReady somehow?

[westonruter]

We could use wp.domReady but this script is already depending on jQuery so we can use jQuery ready instead which does the same thing.

[westonruter]

Ok, issues have been addressed.