add some new surface values (#597)

Author: matkoniecz

data/fields/surface.json

@@ -12,11 +12,16 @@
             "compacted": "Compacted",
             "concrete": "Concrete",
             "paving_stones": "Paving Stones",
+            "sett": "Sett",
             "dirt": "Dirt",
             "grass": "Grass",
             "sand": "Sand",
             "wood": "Wood",
+            "metal": "Metal",
             "artificial_turf": "Artificial Turf",
+            "unhewn_cobblestone": "Cobblestone (uncut, rounded stones)",
+            "mud": "Persistently Muddy",
+            "woodchips": "Woodchips",
             "salt": "Salt"
         }
     }