Fix warnings

The CopyBlock component is throwing warnings about deprecated `defaultProps` (as done in closed PR #131) by using JS default declaration syntax instead. There are also warnings about passing props through to the DOM via `styled-component`. Using a `$` prefix removes this. Closes #165 Closes #104 Closes #163 Closes #138 I was not able to get the tests to run (either before or after editing code), but Storybook renders the component fine, and including it in my app means the warnings no longer show.