Fix #72 by adding gain+cover back into range result object

@matallo This PR adds in gain+cover for supplied ISO or GEOM. The `range` object in the response now looks like this:

```json
   "range":{
      "percent":{
         "value":10.991097801162912,
         "gain":21.351877283895057,
         "units":"Percentage",
         "treecover_2000":86.38793724336855,
         "begin":2008,
         "end":2010,
         "name":"UMD Percentage Loss"
      },
      "area":{
         "value":1146.852974080031,
         "gain":2227.9361359730915,
         "units":"Hectares",
         "treecover_2000":9014.04614392248,
         "begin":2008,
         "end":2010,
         "name":"UMD Hectares Loss"
      }
   }
}
```

Range by ISO:
http://wip.gfw-apis.appspot.com/datasets/hansen?begin=2004&end=2012&layer=loss&iso=bra

Range by GEOM:
http://wip.gfw-apis.appspot.com/datasets/hansen?begin=2004&end=2012&layer=loss&geom={%22type%22:%22Polygon%22,%22coordinates%22:[[[102.65350,-0.73499],[103.75488,-0.89153],[104.14764,-1.57527],[102.77161,-1.47368]]]}&bust=1