schema: change northing and easting to floats

postgresql-simple does not like to convert NUMERIC to floating-point
types.  Ideally we could use Scientific for this, but although
postgresql-simple has instances for Scientific, cassava does not.
Therefore: floating point all the things.
[WIP] add queryParkFacilities function

Add a queryParkFacilities.  All our column/field types are cactus at
the moment - this type checks but it won't work har har!