Refactors google translate integration

Google Translate Widget Dropdown only display mode added in
https://github.com/codeforamerica/ohana-web-search/pull/540 appears to
have been inadvertently removed. This commit re-sets the dropdown mode
to dropdown only.
It's defined in `application.js` when the widget manager is initialized --> https://github.com/codeforamerica/ohana-web-search/blob/google-translate-dropdown/app/assets/javascripts/application.js#L86 ... I don't think this needs to live in settings though, it just needs to be customizable without needing to dig into the google-translate-manager module.