Toggle obscured observations on/off on maps

[henrydelange]

@charlie

In the long term it would be better yet to have obscured things just display as a gridded cell with darker color for more observations (like some eBird displays maybe) and not have points at all. The randomized points continue to cause tons of confusion with new users.

Having a better way to visually tell obscured points apart would be nice. Also points with huge accuracy circles could be shown differently (maybe lighter) - I often find observations with huge accuracy circles, sometimes larger than entire countries.