Show a warning when trying to leave the survey page.
Show a warning when trying to leave the survey page.

azavea/nyc-trees,maurizi/nyc-trees,azavea/nyc-trees,maurizi/nyc-trees,kdeloach/nyc-trees,maurizi/nyc-trees,RickMohr/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,maurizi/nyc-trees,kdeloach/nyc-trees,azavea/nyc-trees,RickMohr/nyc-trees,kdeloach/nyc-trees,kdeloach/nyc-trees,RickMohr/nyc-trees,RickMohr/nyc-trees,azavea/nyc-trees