Introduce scalafx GUI

**Description:** enable scalafx and introduce a helloworld like screen that can be distributed for different operating systems by executing `sbt gui/packageJavafx`.
**Testing:**
![image](https://cloud.githubusercontent.com/assets/259587/3236699/9035289c-f0e0-11e3-9cd9-277eaf543963.png)
![image](https://cloud.githubusercontent.com/assets/259587/3236704/932fbf4e-f0e0-11e3-9794-d169c22e828f.png)
**Coverage:** new `Main` class is not covered.