normalize output to dict format

All new data will be stored as dicts as shown below. Completely backwards compatible with old data.
```
{
   ....
   "my_calc": {
       "total": [
           {
               "date": "2012-12-01",
               "value": 1,
               "group_by": [
                   "test_domain",
                   "user_id1",
                   "group_id1"
               ]
           },
           {
               "date": "2012-12-01",
               "value": 1,
               "group_by": null
           }
       ]
   }
}```