Various Changes

### Various Changes

- [x] Display a preview of the entry body (as a tooltip).
- [x] Display a lock icon near the entry title when the entry is restricted to agents.
- [x] Add a settings to remove the 'agent only' topics from the results

As asked by @maximeprades. Reviews are welcome :)

ps: I think it will conflict with https://github.com/zendesk/answer_suggestions_app/pull/1. I'll push to https://github.com/zendesk/answer_suggestions_app/pull/1 if needed.