- Changed classNames in `Search` component.
- Moved styles from `header.scss` to `search.scss`.
- Deleted `HeaderSearch` and `HeaderSearchButton` components, no longer needed.
- Removed wrapper element around search form.
- Corrected marketplace API address in `Search` component.
- Using state to remember search term, instead of getting value of search input.
- Added condition to clear search input if Escape is pressed while it's focused.
- Not running search if search term is falsy.
- Changed label of "Extensions" tab to "Browse" – we'll do this for the moment, as we have repetition with the page title `Extensions`.