Port Google search

Port over search form and filter components for the header search, search results page and homepage. Rewrite Ruby functions for generating search metatags and JSON schemas as Hugo partials. Use the dev env search API key for now.

• Search form components - !120 (merged)
• Mobile search forms - !122 (merged)
• Results page - !129 (merged)
• Set up redirects (or a temporary redirect handler) so that result links work - !139 (merged), !143 (merged)

Note that Hugo requires special configuration to consume environment variables: https://gohugo.io/functions/os/getenv/#security

We'll handle search-related meta tags in a separate issue: #91 (closed)