Strip all styling from `<button>`

[dtdesign]

The button element is incredibly versatile and benefits from good a11y when used correctly. However, the current default styling creates all sort of issues that makes <button> not feasible in most cases. The alternative is to resort to a[href="#"] with role="button" plus extra event listeners to handle the keyboard interaction.

• [x] Strip the default styling from <button>.
• [x] Disable the default appearance of buttons to make them easier to style.
• [x] Add the .button class to all elements that should continue to look like a button.
• [ ] Convert a[href="#"] into <button>, this includes stripping extra keydown events that are no longer required.
• [ ] Convert non-link buttons (*) into <button>.

(*) Non-link buttons are HTML constructs such as span.pointer that pretend to be buttons but do not fully behave like those.