V4 - Laying the foundation for the button components

[branlok]

Hello,
Like to make a proposal to expand a bit on the component for v4 button component as part of laying the foundation for the future. All observable styles in v3 (and more as v4 expands) will have the styling logic be included in the component by passing the required and optional props. Abstracting and encapsulating a range of styles can safe guard against developer's altering brand design consistency. While it's still possible to cascade styles from parent component, the constraints should make it become the last resort.

Figma link serves as a visual proposal and examples for the few button types and customizability + additional reasoning.
https://www.figma.com/file/zaPBj1kYY7bZ7NTC3HDnkU/Kitsu-Buttons?node-id=10%3A286

I can implement something for review, but if things are already set in stone, it's okay too.