KTX 1.9.4-b2

The first release that contains ktx-app module - ApplicationListener implementation utilities.

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Change log:

• [FEATURE] (ktx-actors) Added Actor.onKeyUp and Actor.onKeyDown extension methods that attach
  EventListener implementations listening to InputEvent instances.
• [FEATURE] (ktx-app) Implemented ktx-app module.
  • KotlinApplication was added as an ApplicationAdapter.
  • clearScreen utility function allows to easily clear the application screen.
  • LetterboxingViewport is a Viewport implementation that combines ScreenViewport and FitViewport behaviors.
• [FEATURE] (ktx-vis) Added ListViewStyle support to ListView factory methods.
• [FEATURE] (ktx-vis) Added top level tab() method.
• [FEATURE] (ktx-vis-style) Added ListViewStyle factory method: listView.
• [FIX] (ktx-scene2d) Added missing TextButton factory methods.