Edit population title

## Story
* https://www.pivotaltracker.com/story/show/75134126

## Notes
* Needs more thorax goodness, less DOM hacking

## Screenshot

![image](https://cloud.githubusercontent.com/assets/2136286/4207709/6dacf7f8-3859-11e4-8875-f57043767973.png)

The most "thoraxy" approach would be to create a micro view for the population, where the view model is the population; then we could use @serialize() to get the data and put it on the population object, refer to the views model to get the population index, etc. rather than going directly to the DOM. That's a bit of a refactoring, but still fairly straightforward, and something we should consider.