Add toggleable neighborhood boundary layer to map

[patcon]

Request from Carolyn via email:

And for the next iteration of the map, we’d love to get the Neighbourhood boundary layer and filter (in addition to the Ward boundary layer) added to the map. There are 140 neighbourhoods in Toronto; you can see them on the Council map here: https://www.toronto.ca/city-government/data-research-maps/neighbourhoods-communities/neighbourhood-profiles/

Like the current ward toggle:

Will need some consideration of what's the best interface (toggles? checkboxes? dropdown?), since the shouldn't both be on at once