* Improve RSS entries for statuses
- Render polls in both accounts and tags serializers
- Refactor RSS serializers
- Change title preview to include ellipsis when truncated
- Change title preview to show CW instead of toot text
- Add tests
* Remove title from OEmbed serialization
Twitter doesn't serialize title either, and tihs allows us to move the
title formatting code to the RSS serializers.
* When serializing polls over OStatus, serialize poll options to text
* Do the same for RSS feeds
* Use “[ ] ” as a prefix for poll options instead of “- ”
