Differentiate between paved/unpaved roads (closes #2564)

Now `iD.svg.TagClasses` will add the class 'tag-unpaved' for unpaved roads.

js/id/core/tags.js

@@ -30,6 +30,17 @@ iD.oneWayTags = {
     }
 };
 
+iD.pavedTags = {
+    'surface': {
+        'paved': true,
+        'asphalt': true,
+        'concrete': true
+    },
+    'tracktype': {
+        'grade1': true
+    }
+};
+
 iD.interestingTag = function (key) {
     return key !== 'attribution' &&
         key !== 'created_by' &&

js/id/svg/tag_classes.js

@@ -79,6 +79,21 @@ iD.svg.TagClasses = function() {
                 classes += ' tag-' + k + ' tag-' + k + '-' + v;
             }
 
+            // For highways, look for surface tagging..
+            if (primary === 'highway') {
+                var paved = (t.highway !== 'track');
+                for (k in t) {
+                    v = t[k];
+                    if (k in iD.pavedTags) {
+                        paved = !!iD.pavedTags[k][v];
+                        break;
+                    }
+                }
+                if (!paved) {
+                    classes += ' tag-unpaved';
+                }
+            }
+
             classes = classes.trim();
 
             if (classes !== value) {