Only trip owner can make change to stop

https://trello.com/c/01eG5bzs/55-only-trip-owner-can-make-change-to-trip-and-its-stops

![only user can make change to trip](https://cloud.githubusercontent.com/assets/3759510/5189934/bcbd7312-74af-11e4-8f76-ae36d3ac470e.gif)