Add the debug module into the standalone build

This enabled using the `debug` module with the standalone build. Debugging appears to work fine, though with one gotcha: you must manually set `window.DEBUG.enabled = true` even after calling `flight.debug.enable()`. So the final setup code needs to be something like this:

```javascript
flight.debug.enable();
DEBUG.enabled = true;
DEBUG.events.logAll();
```

The `debug` module can then be activated by passing the `flight.logger` mixin into components.