[#57,backend,refactor][s]: create a recline.Backend.Base model which other backends inherit from.

* At the moment this added little other than a cleaner structure but will help with change for #57.

src/backend/elasticsearch.js

@@ -19,7 +19,7 @@ this.recline.Backend = this.recline.Backend || {};
   // localhost:9200 with index twitter and type tweet it would be
   //
   // <pre>http://localhost:9200/twitter/tweet</pre>
-  my.ElasticSearch = Backbone.Model.extend({
+  my.ElasticSearch = my.Base.extend({
     _getESUrl: function(dataset) {
       var out = dataset.get('elasticsearch_url');
       if (out) return out;
@@ -39,7 +39,7 @@ this.recline.Backend = this.recline.Backend || {};
             dataType: 'jsonp'
           });
           var dfd = $.Deferred();
-          my.wrapInTimeout(jqxhr).done(function(schema) {
+          this._wrapInTimeout(jqxhr).done(function(schema) {
             // only one top level key in ES = the type so we can ignore it
             var key = _.keys(schema)[0];
             var fieldData = _.map(schema[key].properties, function(dict, fieldName) {