fix private parking icons at wrong zoom i312

[Rovastar]

#312
I am pretty sure that is right but cannot test atm.

[mrwojo]

There should be commas between the [access = *] checks. The private P symbols should be in a separate attachment with lower priority, otherwise a private P could still block a public P. Also, eventually we'll have to properly check for nulls ([access = null]).

The SQL query could differentiate the access types to handle this more cleanly in Carto if such checks become more popular (as suggested in #323). When access is null or ('', 'yes', 'public'), then access is 'INT-yes'. The styles would be more straightforward, like:

  [amenity = 'parking'][access = 'INT-yes'][zoom >= 15]::amenity {
    point-file: url('symbols/parking.p.16.png');
    point-placement: interior;
  }

  [amenity = 'parking'][access != 'INT-yes'][zoom >= 16]::amenity_private {
    point-file: url('symbols/parking_private.p.16.png');
    point-placement: interior;
  }

[gravitystorm]

Closed - as per mrwojo's comments in the first paragraph