Show custom validation message for problems checkbox group
Show custom validation message for problems checkbox group

Fixes #689

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