[#162,backend,model][l]: major commit addressing several parts of the backend / model refactor in #162.

* Now have Dataset setup and manage "memory store"

  * New fetch API as per issue #162 spec
  * dataproxy utilizes useMemoryStore attribute and just implements fetch
  * Switch gdocs to use Memory.Store properly via new useMemoryStore + fetch methodology
  * Memory backend: query function now follows promise API, remove fetch,upsert,delete and add save function to Store object

* Also refactor to remove _source in QueryResult "hits" attribute on all backends but ElasticSearch - cf #159 (note this means ES currently broken)

test/base.js

@@ -19,7 +19,7 @@ var Fixture = {
       {id: 4, date: '2011-05-04', x: 5, y: 10, z: 15, country: 'UK', title: 'fifth', lat:51.58, lon:0},
       {id: 5, date: '2011-06-02', x: 6, y: 12, z: 18, country: 'DE', title: 'sixth', lat:51.04, lon:7.9}
     ];
-    var dataset = recline.Backend.Memory.createDataset(documents, fields);
+    var dataset = new recline.Model.Dataset({records: documents, fields: fields});
     return dataset;
   }
 };