Convenient application baseclass

Hello Adam,

I started using afterburner.fx while familiarizing myself with JavaFX. My test projects had ```App``` classes that looked very similar, except for the title and the instantiation of the root view. This is why I created a small, convenient base class for ```App``` classes. It provides a nice little starting point for a JavaFX application with afterburner.fx, while providing a couple of "hooks" (the ```protected``` methods) for doing extra initialization if needed.

With this base class, the ```App``` class of the igniter archetype could look something like this:

```java
public class App extends FXMLApplication {

	@Override
	protected FXMLView createAppRootView() {
		return new FollowmeView();
	}

	@Override
	protected String getTitle() {
		return "ignitertest.fx v0.0.1-SNAPSHOT";
	}

	public static void main(String[] args) {
		System.setProperty("happyEnding", " Enjoy the flight!");

		launch(args);
	}

}
```