add checkstyle
Merge branch 'master' of ssh://github.com/saxsys/SynchronizeFX

Conflicts:
	example-server/src/main/java/de/saxsys/synchronizefx/example/domain/Board.java
	example-server/src/main/java/de/saxsys/synchronizefx/example/domain/Note.java
	example-server/src/main/java/de/saxsys/synchronizefx/example/domain/Position2D.java
	synchronizefx-core/src/main/java/de/saxsys/synchronizefx/core/exceptions/SynchronizeFXException.java