Docs infinite search results

• Followup from !191 (merged)
• Adds infinite hits instead of pagination (better navigation and better on mobile)
• Adds search results stats
• Adds search refinement list by tag
  • Replace "EE" with "GitLab" https://github.com/algolia/docsearch-configs/pull/329
• Clean up SCSS code (delete default styles imported from the template, fix lint) (for https://gitlab.com/gitlab-com/gitlab-docs/issues/166)
• Do not display hits on init (when the query is empty) => https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/205

Review app: http://docs-infinite-search-results.178.62.207.141.xip.io/search/