remove building_area for school, kindergarden, etc

These keys should not automatically get building=yes added:
amenity/school, amenity/kindergarden,
tourism/picnic_site, tourism/theme_park

Also renamed to "School Grounds" and "Kindergarden Grounds"
for clarity..
Remove building_area from amenity=hospital
Merge branch 'master' of https://github.com/openstreetmap/iD into bhousel