old_contents: 
  
  media_keys = ['file_id', 'file_type', 'contribution_id', 'creator',
  'creator_id', 'created_at', 'url']
  
  comment_keys = ['comment_id', 'contribution_id', 'creator', 'creator_id',
  'created_at', 'respondsto', 'text']
  
  keys = ['geom', 'id', 'creator', 'creator_id', 'created_at', 'status']
  
new_contents: 
  
  media_keys = ['file_id', 'file_type', 'contribution_id', 'creator',
  'creator_id', 'created_at', 'url']
  
  comment_keys = ['comment_id', 'contribution_id', 'creator', 'creator_id',
  'created_at', 'respondsto', 'text']
  
  keys_obs = ['geom', 'id', 'creator', 'creator_id', 'created_at', 'status']
  
subject: change name for observation keys