[model,refator][s]: reintroduce summary on Record object deprecating recordSummary on Dataset.

* Reverses change in 1dadc1106b
* Record now has fields attribute passed down from Dataset. This is needed in order to support summary method and also makes sense -- as pointed out by @zephod
* Update examples

src/view.timeline.js

@@ -102,7 +102,7 @@ my.Timeline = Backbone.View.extend({
         "startDate": start,
         "endDate": end,
         "headline": String(record.get('title') || ''),
-        "text": record.get('description') || this.model.recordSummary(record)
+        "text": record.get('description') || record.summary()
       };
       return tlEntry;
     } else {