Helper methods and classes to simplify ScalaFX use.

Package [[org.scalafx.extras `org.scalafx.extras`]] contains basic helper methods for running tasks on threads and
showing messages.

Package [[org.scalafx.extras.image `org.scalafx.extras.image`]] contains image display component with scrolling and zooming.

Package [[org.scalafx.extras.mvcfx `org.scalafx.extras.mvcfx`]] contains classes for creating with UI components
based on FXML.