Fixes #90 - steward carousel

- Makes the Steward and Trail next/prev buttons act like a carousel, so
that when they reach the end or beginning they loop around to the
beginning or end.
- Also hides the chevron arrows for the trails when there is only 1 of
1 trails.

![screen shot 2014-05-12 at 2 41 31 am](https://cloud.githubusercontent.com/assets/704760/2942782/a28d3798-d9b9-11e3-8034-6e8ff540213d.png)

![screen shot 2014-05-12 at 2 41 09 am](https://cloud.githubusercontent.com/assets/704760/2942784/a28e579a-d9b9-11e3-8741-201086b7aeb8.png)

![screen shot 2014-05-12 at 2 40 54 am](https://cloud.githubusercontent.com/assets/704760/2942783/a28d7c76-d9b9-11e3-9271-daef2456809c.png)

@alanjosephwilliams ready for review and merge!