Set title attribute for tag keys/values, ensure combo options have title

This will show values as hover tooltips, in case the field is too narrow and the value is cut off.
(closes #3054)

js/id/services/taginfo.js

@@ -44,12 +44,17 @@ iD.services.taginfo = function() {
         return function(d) { return parseFloat(d.fraction) > 0.01 || d.in_wiki; };
     }
 
-    function valKey(d) { return { value: d.key }; }
+    function valKey(d) {
+        return {
+            value: d.key,
+            title: d.key
+        };
+    }
 
     function valKeyDescription(d) {
         return {
             value: d.value,
-            title: d.description
+            title: d.description || d.value
         };
     }
 

js/id/ui/raw_tag_editor.js

@@ -100,11 +100,13 @@ iD.ui.RawTagEditor = function(context) {
         });
 
         $items.select('input.key')
+            .attr('title', function(d) { return d.key; })
             .value(function(d) { return d.key; })
             .on('blur', keyChange)
             .on('change', keyChange);
 
         $items.select('input.value')
+            .attr('title', function(d) { return d.value; })
             .value(function(d) { return d.value; })
             .on('blur', valueChange)
             .on('change', valueChange)