WIP: Truth API for validation

@danhammer 

Checkout this repo, download Google App Engine runtime [here](https://commondatastorage.googleapis.com/appengine-sdks/featured/google_appengine_1.9.0.zip), unzip and put it on your path, then:

```bash
$ cd gfw-api
$ dev_appserver.py --clear_datastore=1 --show_mail_body=1 .
```

Then hit this endpoint:

[http://localhost:8080/truth?ll=1,2&dim=200,300&asset=l8&date=2013-03-14&bust=1](http://localhost:8080/truth?ll=1,2&dim=200,300&asset=l8&date=2013-03-14&bust=1)

BOOM