[#34,query][s]: rename offset to from on query object.

* More natural in fact and we may as well go whole hog with ES structure.

src/backend/memory.js

@@ -80,7 +80,7 @@ this.recline.Backend = this.recline.Backend || {};
     },
     query: function(model, queryObj) {
       var numRows = queryObj.size;
-      var start = queryObj.offset;
+      var start = queryObj.from;
       var dfd = $.Deferred();
       results = this.datasets[model.id].documents;
       // not complete sorting!

src/backend/webstore.js

@@ -40,7 +40,7 @@ this.recline.Backend = this.recline.Backend || {};
       var base = model.get('webstore_url');
       var data = {
         _limit:  queryObj.size
-        , _offset: queryObj.offset
+        , _offset: queryObj.from
       };
       var jqxhr = $.ajax({
         url: base + '.json',