add feature and hidden listings logic

[sparrowDom]

Checklist:

• [x] Ensure all new and existing tests pass
• [x] Update any relevant READMEs and docs

Description:

Reads hidden/featured listings from gist file and considers them when returning search results from elasticsearch. Hidden listings are omitted from results, featured listings are returned at the top of the search results and marked as featured. Query and filters still apply to featured listings, they are just always sorted at the top.

Important:

• [ ] currently there are 2 gist files and are tied to my account (sparrowDom) This should be changed to someone more core to origin team, and/or someone who will be in charge of hiding/featuring listings. Before merge we should change that.
• Gist file links point to a specific version of file. For that reason rawgit.com service is used, that always redirects to latest version of file in gist. It is important that we use production rawgit links that update less frequently and are not limited by the number of requests.

Solves issue: https://github.com/OriginProtocol/origin-dapp/issues/594 Connected Pull Request:https://github.com/OriginProtocol/origin-dapp/pull/617

[micahalcorn]

Closing in accordance with https://github.com/OriginProtocol/origin/pull/617 🚪