feat!: refactor Admin UX/UI

[justlevine]

What

This PR contains a complete refactor of packages/admin, along with the storage/handling of plugin settings.

More specifically:

Todo:

• Add path aliases to tsconfig
• Rename file structure to use kebab-case
• Clean up components/layouts/screen
• Redesign header
• Add custom settings store + REST endpoint
• Refactor settings schema + screens for composability (DRY/SOLID)
• Refactor settings registration
• Settings migration on update

Why

Unblocks the UX issues + scalability for #129

How

Testing Instructions

Additional Info

Checklist:

• My code is tested to the best of my abilities.
• My code follows the WordPress Coding Standards.
• My code has proper inline documentation.
• I have added unit tests to verify the code works as intended.
• I included the relevant changes in CHANGELOG.md

[coveralls]

coverage: 71.653% (-10.3%) from 81.924%
when pulling 46ae7a1 on feat/refactor-admin
into 72936f4 on develop.