Move box-sizing to each components css file

[mimarz]

Now box-sizing: border-box is set in .ds-reset.
This has some issues:

• If class names are hashed in the future (CSS modules) for CSS versioning, the [class^="ds-"] will break
• If using CSS without React, a consumer can add class="my-button ds-button", making [class^="ds-"] break
• It is a "transparent" dependency - meaning a developer can not open i.e. button.css and see the complete styling
  Even though this means repeating box-sizing in several files, it is a more robust and explicit solution