split API config into URL and endpoint

Could whomever merges this into master please ensure this gets run:

    heroku config:set --app lr-feeder-app AUTHENTICATED_SEARCH_API_URL=http://lr-search-api.herokuapp.com
    heroku config:set --app lr-feeder-app AUTHENTICATED_SEARCH_API_ENDPOINT=/load/authenticated_titles
    heroku config:set --app lr-feeder-app PUBLIC_SEARCH_API_URL=http://lr-search-api.herokuapp.com
    heroku config:set --app lr-feeder-app PUBLIC_SEARCH_API_ENDPOINT=/load/public_titles