Hide early nursing_home to zoom 15

[nvkelso]

            hide-until-z15-with-area:
                filter:
                    area: true
                    $zoom: { max: 15 }
                    kind: [nursing_home]
                draw:
                    mapzen_icon_library:
                        visible: false

[nvkelso]

Example: https://www.openstreetmap.org/way/267296981

Note that the v1.5 build of Nextzen tiles has this in a weird state, but the current version of the way above does match the test example and was the original reason for the stylesheet hack.

[nvkelso]

Probably the min should be 15 in the pois.yaml instead of 0, call it done?

[nvkelso]

Verified.