Support a custom survey prompt with survey.surveyOptions.prompt

If `survey.surveyOptions.prompt` is set, it will override all other prompts for the first entry. 

For future entries, the "Select another location to continue" prompt will continue to be used for simplicity. 

![screen shot 2014-12-20 at 4 08 24 pm](https://cloud.githubusercontent.com/assets/86435/5516298/c1b5b8ea-8862-11e4-84c0-3cb61deb7a1f.png)