Add maven defaultGoal to all projects to ease first usage

[ottlinger]

I just read your JavaMagazin article and wanted to play with some of the examples and checked out the repository.

Personally I'd consider it to be cool if all of the subdirectories would have a defaultGoal set in pom.xml.

Asteroids doesn't seem to run via mvn javafx:run but I had to do a mvn package and start the created JAR with java -jar, while GeometryWars was able to run via javafx:run.

Integrating a defaultGoal is quite easy and would allow anyone to just clone the repo and hit 'mvn' to see the game running.

Thanks for your great work and the cool library!