1.3.1

This is a small release with two fixes for problems introduced with the last version 1.3.0.

• Due to the fix for #240 some users had breaking unit tests because of a "toolkit not initialized" Exception when publish/subscribe of the ViewModel was part of the JUnit test. We are now checking if there is a JavaFX UI thread present or not. If no UI thread is present (f.e. while running JUnit tests), the notifications will be published on the current thread like it was done before. This way we can support easy unit tests and still make sure that at runtime all notifications are published on the UI thread. (#263)
• Additionally we have introduced a NotificationTestHelper that can be used to test notifications. The test helper can even be used for use cases where notifications are send from different threads and it will handle the UI thread accordingly. See the new paragraph in the Wiki for more informations: https://github.com/sialcasa/mvvmFX/wiki/NotificationCenter#testing-notifications
• There was a problem with the getHighestMessage method of the ValidationStatus class introduced with #194. In some cases inside of ChangeListeners on the validProperty or one of the observable lists of validation messages, the getHighestMessage was throwing IndexOutOfBoundExceptions. We have now a new implementation for this method that fixes the problems. (#264)