User can preview and flag a survey
- Add a preview page with a map that rendered the GeoJSON of the last survey for a given user
- Update styles for the map and buttons
- Update links to and from the preview page
- Add function to fetch the GeoJSON of the last survey
- Add function to flag a survey on CartoDB
Update the style of the preview vectors
Merge pull request #29 from openplans/flag-survey

User can preview and flag a survey if it looks wrong