Add missing values for artwork_type

Add some of the used and documented values from OSM wiki

Author: okainov

data/fields/artwork_type.json

@@ -12,6 +12,10 @@
             "bust": "Bust",
             "painting": "Painting",
             "mosaic": "Mosaic",
+            "tilework": "Tile work",
+            "stone": "Stone",
+            "dwarf": "Dwarf",
+            "street_art": "Street-art",
             "relief": "Relief"
         }
     }