Application may be a class

https://github.com/strongloop/express/blob/5.0/lib/application.js

The fact is that `lib/application.js` may perfectly export the constructor of a "real" `Application` class, and define its prototype as usual instead of `var app = exports = module.exports = {};`. I mean:

```
module.exports = Application;

function Application() {
var router = null;

this.cache = {};
this.settings = {};
this.engines = {};
this.defaultConfiguration();

etc etc
}

Application.prototype.defaultConfiguration = function() {
...
};

Application.prototype.handle = function(req, res, done) {
...
};
```

I don't see any downside in doing it that way, do I miss something? At the end the new `Router` class is now designed as a "real" JavaScript class.