Chen show all trips

https://trello.com/c/YzXae8PK/35-as-a-user-i-can-see-all-trips

- generate Trip model
- generate Trip controller
- add trip index action and page
- only user can see all trips (require login)

![show all trips](https://cloud.githubusercontent.com/assets/3759510/5073021/ee94bf4e-6e4c-11e4-8f2c-2cbfd342d6ba.gif)