Switch to ST_PointOnSurface

Resolves gravitystorm#1644.

This is a necessary step towards vector rendering (see gravitystorm#1644).

This is a second trial of gravitystorm#3228, based on the word by @pnorman in gravitystorm#3233.

This is a first step, once we have this than we can probably merge the point and poly layers (for example amenity-points and amenity-points-poly).

addressing.mss

@@ -25,7 +25,6 @@
         }
       }
     }
-    text-placement: interior;
     text-face-name: @book-fonts;
     text-fill: @address-color;
     text-halo-radius: @standard-halo-radius;
@@ -56,7 +55,6 @@ no official postal addresses) */
   [zoom >= 14][way_pixels > 3000],
   [zoom >= 17] {
     text-name: "[name]";
-    text-placement: interior;
     text-face-name: @book-fonts;
     text-fill: #444;
     text-halo-radius: @standard-halo-radius;