Redesign search

Created by: tysongach

• Moved the search into the main content header to make better use of vertical space in the layout.
• Search is now visually (and in the DOM) after the page title, which makes for a more logical and expected flow because it is a page-based search.
• Improved accessibility:
  • Navigating the search via keyboard now works in Safari.
  • Meaningful accessible names and labels were added.
  • Include the name of the resource being searched in labels.
• Reduced the CSS needed for search by 44%.
• Remove unnecessary content_for helper that wrapped the rendering of the search partial.

Note: This PR depends on #880 being merged.

Before

After