Remove need for testing boiler plate.

Currently apps require code like:

```javascript
if (typeof api === "undefined") {
   // testing hook (supplies api when it is not passed in by the real sandbox)
   var api = this.api = new vumigo.dummy_api.DummyApi();
}
```

in order for tests to run. Ideally the dummy API should be injected in some way similar to what the real sandbox does (i.e. by starting a new JS context and putting the dummy API inside it).