Group same contributions without URL, make grouping more precise

app/models/contribution.js

@@ -47,9 +47,10 @@ export default EmberObject.extend({
   }),
 
   // Stable key shared by all per-contributor contributions created for the
-  // same issue/pull request (derived from `url`). Manual contributions without
-  // a URL return null and are treated as singletons (not grouped).
-  groupId: computed('url', function() {
+  // same piece of work (derived from `url`, `description`, `date`, `amount`,
+  // and `kind`). Contributions without enough fields to derive a key return
+  // null and are treated as singletons (not grouped).
+  groupId: computed('url', 'description', 'date', 'amount', 'kind', function() {
     return contributionGroupingKey(this);
   }),