Add grade 1 tracks to paved (#1485)

This PR sets `surface=paved` for `highway=track` + `tracktype=grade1` if no other value of `surface` is set.  Roads tagged in this way are [generally paved](https://wiki.openstreetmap.org/wiki/Key:tracktype) and therefore encoding them as a paved road is appropriate.

layers/transportation/mapping.yaml

@@ -180,6 +180,9 @@ tables:
     - name: construction
       key: construction
       type: string
+    - name: tracktype
+      key: tracktype
+      type: string
     - *ref
     - *network
     - *z_order