Feature/stop insertion

This PR adds dragging and some more interface options to scenario stop creation

![screen shot 2014-12-01 at 2 32 03 pm 2](https://cloud.githubusercontent.com/assets/1977405/5251900/1c4a1d74-7967-11e4-84e4-e60721c75db3.png)

What happens if a user enters an invalid number/value/string/etc?