* refactor: Convert pixelated borders from box-shadows to border-images
Our previous usage of `box-shadows` and pseudo elements proved to be pretty buggy. Converting to
`border-image`s seems to have fixed a lot of the issues that `box-shadows` caused, such as
`background-color`s appering over top of our borders.
BREAKING CHANGE: This change both eliminates pseudo elements from several components, and adds
pseudo elements to components that did not have them before. This could cause compatibility issues
for users that relied on the existence of those pseudo elements for various styling techniques.
* style(buttons): Remove superfluous commented code
* feat(progress.scss): add progress bar element
* feat(progress.stories.js): add progress test in storybook
* feat: add is-filled class
* feat: add color variation
